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 $54.52   7.580%   $58.6526   $58.65   $58.65   $58.70  
  Purchase #2 $151.76   8.801%   $165.1164   $165.12   $165.10   $165.10  
  Purchase #3 $155.92   6.548%   $166.1296   $166.13   $166.15   $166.10  
  Purchase #4 $69.39   9.204%   $75.7767   $75.78   $75.80   $75.80  
  Purchase #5 $183.38   10.585%   $202.7908   $202.79   $202.80   $202.80  
  Purchase #6 $231.61   3.237%   $239.1072   $239.11   $239.10   $239.10  
  Purchase #7 $41.92   13.445%   $47.5561   $47.56   $47.55   $47.60  
  7 purchase totals = $888.50       $955.1294   $955.14   $955.15   $955.20