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 $67.65   10.191%   $74.5442   $74.54   $74.55   $74.50  
  Purchase #2 $239.69   6.678%   $255.6965   $255.70   $255.70   $255.70  
  Purchase #3 $209.87   6.365%   $223.2282   $223.23   $223.25   $223.20  
  Purchase #4 $141.41   13.127%   $159.9729   $159.97   $159.95   $160.00  
  Purchase #5 $27.66   13.450%   $31.3803   $31.38   $31.40   $31.40  
  Purchase #6 $95.68   11.842%   $107.0104   $107.01   $107.00   $107.00  
  Purchase #7 $177.62   9.750%   $194.938   $194.94   $194.95   $194.90  
  7 purchase totals = $959.58       $1,046.7705   $1,046.77   $1,046.80   $1,046.70