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 $12.71   11.701%   $14.1972   $14.20   $14.20   $14.20  
  Purchase #2 $227.85   9.726%   $250.0107   $250.01   $250.00   $250.00  
  Purchase #3 $126.32   12.685%   $142.3437   $142.34   $142.35   $142.30  
  Purchase #4 $173.36   8.852%   $188.7058   $188.71   $188.70   $188.70  
  Purchase #5 $103.69   9.754%   $113.8039   $113.80   $113.80   $113.80  
  Purchase #6 $226.39   3.609%   $234.5604   $234.56   $234.55   $234.60  
  Purchase #7 $91.29   10.175%   $100.5788   $100.58   $100.60   $100.60  
  7 purchase totals = $961.61       $1,044.2005   $1,044.20   $1,044.20   $1,044.20