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 $47.38   13.542%   $53.7962   $53.80   $53.80   $53.80  
  Purchase #2 $91.26   4.659%   $95.5118   $95.51   $95.50   $95.50  
  Purchase #3 $235.47   13.593%   $267.4774   $267.48   $267.50   $267.50  
  Purchase #4 $166.89   4.760%   $174.834   $174.83   $174.85   $174.80  
  Purchase #5 $57.92   10.288%   $63.8788   $63.88   $63.90   $63.90  
  Purchase #6 $151.25   12.352%   $169.9324   $169.93   $169.95   $169.90  
  Purchase #7 $239.78   11.630%   $267.6664   $267.67   $267.65   $267.70  
  7 purchase totals = $989.95       $1,093.0970   $1,093.10   $1,093.15   $1,093.10