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 $132.60   11.581%   $147.9564   $147.96   $147.95   $148.00  
  Purchase #2 $207.38   8.858%   $225.7497   $225.75   $225.75   $225.70  
  Purchase #3 $180.40   7.685%   $194.2637   $194.26   $194.25   $194.30  
  Purchase #4 $73.42   8.471%   $79.6394   $79.64   $79.65   $79.60  
  Purchase #5 $71.95   5.363%   $75.8087   $75.81   $75.80   $75.80  
  Purchase #6 $92.96   12.683%   $104.7501   $104.75   $104.75   $104.80  
  Purchase #7 $226.94   6.737%   $242.2289   $242.23   $242.25   $242.20  
  7 purchase totals = $985.65       $1,070.3969   $1,070.40   $1,070.40   $1,070.40