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 $74.98   10.145%   $82.5867   $82.59   $82.60   $82.60  
  Purchase #2 $95.87   11.643%   $107.0321   $107.03   $107.05   $107.00  
  Purchase #3 $226.45   6.640%   $241.4863   $241.49   $241.50   $241.50  
  Purchase #4 $189.91   10.398%   $209.6568   $209.66   $209.65   $209.70  
  Purchase #5 $241.49   8.795%   $262.729   $262.73   $262.75   $262.70  
  Purchase #6 $81.35   12.714%   $91.6928   $91.69   $91.70   $91.70  
  Purchase #7 $44.66   4.560%   $46.6965   $46.70   $46.70   $46.70  
  7 purchase totals = $954.71       $1,041.8802   $1,041.89   $1,041.95   $1,041.90