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 $227.53   10.763%   $252.0191   $252.02   $252.00   $252.00  
  Purchase #2 $123.72   9.356%   $135.2952   $135.30   $135.30   $135.30  
  Purchase #3 $247.39   7.557%   $266.0853   $266.09   $266.10   $266.10  
  Purchase #4 $182.58   12.130%   $204.727   $204.73   $204.75   $204.70  
  Purchase #5 $160.46   9.199%   $175.2207   $175.22   $175.20   $175.20  
  Purchase #6 $181.47   3.463%   $187.7543   $187.75   $187.75   $187.80  
  Purchase #7 $115.88   9.745%   $127.1725   $127.17   $127.15   $127.20  
  7 purchase totals = $1,239.03       $1,348.2741   $1,348.28   $1,348.25   $1,348.30