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 $51.96   13.818%   $59.1398   $59.14   $59.15   $59.10  
  Purchase #2 $24.74   9.189%   $27.0134   $27.01   $27.00   $27.00  
  Purchase #3 $93.67   3.535%   $96.9812   $96.98   $97.00   $97.00  
  Purchase #4 $234.54   9.410%   $256.6102   $256.61   $256.60   $256.60  
  Purchase #5 $63.98   9.862%   $70.2897   $70.29   $70.30   $70.30  
  Purchase #6 $108.56   8.548%   $117.8397   $117.84   $117.85   $117.80  
  Purchase #7 $25.48   7.330%   $27.3477   $27.35   $27.35   $27.30  
  7 purchase totals = $602.93       $655.2217   $655.22   $655.25   $655.10