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 $201.43   10.718%   $223.0193   $223.02   $223.00   $223.00  
  Purchase #2 $142.53   11.672%   $159.1661   $159.17   $159.15   $159.20  
  Purchase #3 $26.98   6.120%   $28.6312   $28.63   $28.65   $28.60  
  Purchase #4 $108.88   11.638%   $121.5515   $121.55   $121.55   $121.60  
  Purchase #5 $58.95   7.685%   $63.4803   $63.48   $63.50   $63.50  
  Purchase #6 $8.82   3.701%   $9.1464   $9.15   $9.15   $9.10  
  Purchase #7 $121.83   4.372%   $127.1564   $127.16   $127.15   $127.20  
  7 purchase totals = $669.42       $732.1512   $732.16   $732.15   $732.20