Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.43   12.230%   $270.9569   $270.96   $270.95   $271.00  
  Purchase #2 $210.39   7.625%   $226.4322   $226.43   $226.45   $226.40  
  Purchase #3 $119.59   3.325%   $123.5664   $123.57   $123.55   $123.60  
  Purchase #4 $206.49   10.553%   $228.2809   $228.28   $228.30   $228.30  
  Purchase #5 $178.75   12.641%   $201.3458   $201.35   $201.35   $201.30  
  Purchase #6 $209.63   11.388%   $233.5027   $233.50   $233.50   $233.50  
  Purchase #7 $180.46   5.565%   $190.5026   $190.50   $190.50   $190.50  
  7 purchase totals = $1,346.74       $1,474.5875   $1,474.59   $1,474.60   $1,474.60