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 $205.64   6.295%   $218.585   $218.59   $218.60   $218.60  
  Purchase #2 $56.89   11.348%   $63.3459   $63.35   $63.35   $63.30  
  Purchase #3 $242.58   5.720%   $256.4556   $256.46   $256.45   $256.50  
  Purchase #4 $209.67   12.236%   $235.3252   $235.33   $235.35   $235.30  
  Purchase #5 $44.97   12.314%   $50.5076   $50.51   $50.50   $50.50  
  Purchase #6 $63.54   7.705%   $68.4358   $68.44   $68.45   $68.40  
  Purchase #7 $46.48   5.792%   $49.1721   $49.17   $49.15   $49.20  
  7 purchase totals = $869.77       $941.8272   $941.85   $941.85   $941.80