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 $211.29   3.426%   $218.5288   $218.53   $218.55   $218.50  
  Purchase #2 $97.90   3.280%   $101.1111   $101.11   $101.10   $101.10  
  Purchase #3 $91.30   5.319%   $96.1562   $96.16   $96.15   $96.20  
  Purchase #4 $58.72   8.530%   $63.7288   $63.73   $63.75   $63.70  
  Purchase #5 $97.64   11.799%   $109.1605   $109.16   $109.15   $109.20  
  Purchase #6 $84.49   9.394%   $92.427   $92.43   $92.45   $92.40  
  Purchase #7 $245.29   7.125%   $262.7669   $262.77   $262.75   $262.80  
  7 purchase totals = $886.63       $943.8793   $943.89   $943.90   $943.90