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 $234.69   3.167%   $242.1226   $242.12   $242.10   $242.10  
  Purchase #2 $166.84   9.198%   $182.1859   $182.19   $182.20   $182.20  
  Purchase #3 $41.67   4.112%   $43.3835   $43.38   $43.40   $43.40  
  Purchase #4 $52.79   5.246%   $55.5594   $55.56   $55.55   $55.60  
  Purchase #5 $185.86   9.113%   $202.7974   $202.80   $202.80   $202.80  
  Purchase #6 $115.81   12.267%   $130.0164   $130.02   $130.00   $130.00  
  Purchase #7 $197.57   10.276%   $217.8723   $217.87   $217.85   $217.90  
  7 purchase totals = $995.23       $1,073.9375   $1,073.94   $1,073.90   $1,074.00