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 $101.47   10.386%   $112.0087   $112.01   $112.00   $112.00  
  Purchase #2 $160.91   3.307%   $166.2313   $166.23   $166.25   $166.20  
  Purchase #3 $228.55   11.449%   $254.7167   $254.72   $254.70   $254.70  
  Purchase #4 $43.66   4.346%   $45.5575   $45.56   $45.55   $45.60  
  Purchase #5 $136.33   3.793%   $141.501   $141.50   $141.50   $141.50  
  Purchase #6 $14.65   11.859%   $16.3873   $16.39   $16.40   $16.40  
  Purchase #7 $22.57   13.117%   $25.5305   $25.53   $25.55   $25.50  
  7 purchase totals = $708.14       $761.9330   $761.94   $761.95   $761.90