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 $110.59   5.607%   $116.7908   $116.79   $116.80   $116.80  
  Purchase #2 $70.93   3.265%   $73.2459   $73.25   $73.25   $73.20  
  Purchase #3 $155.41   7.174%   $166.5591   $166.56   $166.55   $166.60  
  Purchase #4 $197.37   8.313%   $213.7774   $213.78   $213.80   $213.80  
  Purchase #5 $124.84   8.290%   $135.1892   $135.19   $135.20   $135.20  
  Purchase #6 $155.92   7.461%   $167.5532   $167.55   $167.55   $167.60  
  Purchase #7 $80.85   6.143%   $85.8166   $85.82   $85.80   $85.80  
  7 purchase totals = $895.91       $958.9322   $958.94   $958.95   $959.00