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 $87.44   10.299%   $96.4454   $96.45   $96.45   $96.40  
  Purchase #2 $66.73   4.443%   $69.6948   $69.69   $69.70   $69.70  
  Purchase #3 $76.95   7.285%   $82.5558   $82.56   $82.55   $82.60  
  Purchase #4 $60.40   9.644%   $66.225   $66.23   $66.25   $66.20  
  Purchase #5 $177.49   13.736%   $201.87   $201.87   $201.85   $201.90  
  Purchase #6 $14.96   10.776%   $16.5721   $16.57   $16.55   $16.60  
  Purchase #7 $128.89   6.543%   $137.3233   $137.32   $137.30   $137.30  
  7 purchase totals = $612.86       $670.6864   $670.69   $670.65   $670.70