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 $186.59   4.122%   $194.2812   $194.28   $194.30   $194.30  
  Purchase #2 $82.65   12.317%   $92.83   $92.83   $92.85   $92.80  
  Purchase #3 $107.74   10.281%   $118.8167   $118.82   $118.80   $118.80  
  Purchase #4 $63.57   3.495%   $65.7918   $65.79   $65.80   $65.80  
  Purchase #5 $191.69   8.134%   $207.2821   $207.28   $207.30   $207.30  
  Purchase #6 $22.65   10.165%   $24.9524   $24.95   $24.95   $25.00  
  Purchase #7 $232.40   5.848%   $245.9908   $245.99   $246.00   $246.00  
  7 purchase totals = $887.29       $949.9450   $949.94   $950.00   $950.00