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 $120.94   4.610%   $126.5153   $126.52   $126.50   $126.50  
  Purchase #2 $70.28   3.324%   $72.6161   $72.62   $72.60   $72.60  
  Purchase #3 $191.71   5.295%   $201.861   $201.86   $201.85   $201.90  
  Purchase #4 $240.30   6.561%   $256.0661   $256.07   $256.05   $256.10  
  Purchase #5 $87.92   10.322%   $96.9951   $97.00   $97.00   $97.00  
  Purchase #6 $49.92   8.292%   $54.0594   $54.06   $54.05   $54.10  
  Purchase #7 $151.42   4.116%   $157.6524   $157.65   $157.65   $157.70  
  7 purchase totals = $912.49       $965.7654   $965.78   $965.70   $965.90