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 $68.67   10.594%   $75.9449   $75.94   $75.95   $75.90  
  Purchase #2 $133.82   11.817%   $149.6335   $149.63   $149.65   $149.60  
  Purchase #3 $157.86   5.171%   $166.0229   $166.02   $166.00   $166.00  
  Purchase #4 $185.97   8.296%   $201.3981   $201.40   $201.40   $201.40  
  Purchase #5 $179.38   8.662%   $194.9179   $194.92   $194.90   $194.90  
  Purchase #6 $201.78   13.666%   $229.3553   $229.36   $229.35   $229.40  
  Purchase #7 $42.50   10.699%   $47.0471   $47.05   $47.05   $47.00  
  7 purchase totals = $969.98       $1,064.3197   $1,064.32   $1,064.30   $1,064.20