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 $113.40   4.578%   $118.5915   $118.59   $118.60   $118.60  
  Purchase #2 $224.56   11.720%   $250.8784   $250.88   $250.90   $250.90  
  Purchase #3 $55.67   12.162%   $62.4406   $62.44   $62.45   $62.40  
  Purchase #4 $220.73   12.714%   $248.7936   $248.79   $248.80   $248.80  
  Purchase #5 $155.82   8.685%   $169.353   $169.35   $169.35   $169.40  
  Purchase #6 $151.83   8.809%   $165.2047   $165.20   $165.20   $165.20  
  Purchase #7 $55.52   5.828%   $58.7557   $58.76   $58.75   $58.80  
  7 purchase totals = $977.53       $1,074.0175   $1,074.01   $1,074.05   $1,074.10