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 $245.41   12.593%   $276.3145   $276.31   $276.30   $276.30  
  Purchase #2 $211.85   8.129%   $229.0713   $229.07   $229.05   $229.10  
  Purchase #3 $64.41   9.501%   $70.5296   $70.53   $70.55   $70.50  
  Purchase #4 $235.94   4.715%   $247.0646   $247.06   $247.05   $247.10  
  Purchase #5 $83.50   13.108%   $94.4452   $94.45   $94.45   $94.40  
  Purchase #6 $104.48   7.335%   $112.1436   $112.14   $112.15   $112.10  
  Purchase #7 $228.52   3.671%   $236.909   $236.91   $236.90   $236.90  
  7 purchase totals = $1,174.11       $1,266.4778   $1,266.47   $1,266.45   $1,266.40