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 $86.65   8.285%   $93.829   $93.83   $93.85   $93.80  
  Purchase #2 $171.76   11.148%   $190.9078   $190.91   $190.90   $190.90  
  Purchase #3 $138.56   4.241%   $144.4363   $144.44   $144.45   $144.40  
  Purchase #4 $124.48   8.637%   $135.2313   $135.23   $135.25   $135.20  
  Purchase #5 $169.87   9.233%   $185.5541   $185.55   $185.55   $185.60  
  Purchase #6 $139.60   8.861%   $151.97   $151.97   $151.95   $152.00  
  Purchase #7 $37.95   3.252%   $39.1841   $39.18   $39.20   $39.20  
  7 purchase totals = $868.87       $941.1126   $941.11   $941.15   $941.10