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 $91.77   3.211%   $94.7167   $94.72   $94.70   $94.70  
  Purchase #2 $190.57   3.526%   $197.2895   $197.29   $197.30   $197.30  
  Purchase #3 $121.43   3.647%   $125.8586   $125.86   $125.85   $125.90  
  Purchase #4 $77.28   5.277%   $81.3581   $81.36   $81.35   $81.40  
  Purchase #5 $41.93   6.663%   $44.7238   $44.72   $44.70   $44.70  
  Purchase #6 $10.27   7.534%   $11.0437   $11.04   $11.05   $11.00  
  Purchase #7 $175.69   11.107%   $195.2039   $195.20   $195.20   $195.20  
  7 purchase totals = $708.94       $750.1943   $750.19   $750.15   $750.20