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 $224.56   6.117%   $238.2963   $238.30   $238.30   $238.30  
  Purchase #2 $179.78   7.773%   $193.7543   $193.75   $193.75   $193.80  
  Purchase #3 $147.52   3.509%   $152.6965   $152.70   $152.70   $152.70  
  Purchase #4 $241.82   10.184%   $266.4469   $266.45   $266.45   $266.40  
  Purchase #5 $37.99   11.814%   $42.4781   $42.48   $42.50   $42.50  
  Purchase #6 $85.96   8.388%   $93.1703   $93.17   $93.15   $93.20  
  Purchase #7 $241.41   10.263%   $266.1859   $266.19   $266.20   $266.20  
  7 purchase totals = $1,159.04       $1,253.0283   $1,253.04   $1,253.05   $1,253.10