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 $114.35   7.412%   $122.8256   $122.83   $122.85   $122.80  
  Purchase #2 $178.96   6.654%   $190.868   $190.87   $190.85   $190.90  
  Purchase #3 $86.37   7.850%   $93.15   $93.15   $93.15   $93.20  
  Purchase #4 $201.34   11.315%   $224.1216   $224.12   $224.10   $224.10  
  Purchase #5 $66.88   3.213%   $69.0289   $69.03   $69.05   $69.00  
  Purchase #6 $216.99   5.772%   $229.5147   $229.51   $229.50   $229.50  
  Purchase #7 $81.84   11.283%   $91.074   $91.07   $91.05   $91.10  
  7 purchase totals = $946.73       $1,020.5828   $1,020.58   $1,020.55   $1,020.60