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 $65.46   4.720%   $68.5497   $68.55   $68.55   $68.50  
  Purchase #2 $50.25   8.291%   $54.4162   $54.42   $54.40   $54.40  
  Purchase #3 $134.29   11.462%   $149.6823   $149.68   $149.70   $149.70  
  Purchase #4 $58.58   7.657%   $63.0655   $63.07   $63.05   $63.10  
  Purchase #5 $149.69   11.294%   $166.596   $166.60   $166.60   $166.60  
  Purchase #6 $12.98   8.508%   $14.0843   $14.08   $14.10   $14.10  
  Purchase #7 $51.59   12.433%   $58.0042   $58.00   $58.00   $58.00  
  7 purchase totals = $522.84       $574.3982   $574.40   $574.40   $574.40