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 $55.84   11.587%   $62.3102   $62.31   $62.30   $62.30  
  Purchase #2 $194.73   5.368%   $205.1831   $205.18   $205.20   $205.20  
  Purchase #3 $225.85   13.446%   $256.2178   $256.22   $256.20   $256.20  
  Purchase #4 $22.25   5.795%   $23.5394   $23.54   $23.55   $23.50  
  Purchase #5 $114.26   8.656%   $124.1503   $124.15   $124.15   $124.20  
  Purchase #6 $215.45   7.663%   $231.9599   $231.96   $231.95   $232.00  
  Purchase #7 $58.72   12.466%   $66.04   $66.04   $66.05   $66.00  
  7 purchase totals = $887.10       $969.4007   $969.40   $969.40   $969.40