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 $91.75   4.725%   $96.0852   $96.09   $96.10   $96.10  
  Purchase #2 $61.27   8.563%   $66.5166   $66.52   $66.50   $66.50  
  Purchase #3 $235.98   4.496%   $246.5897   $246.59   $246.60   $246.60  
  Purchase #4 $236.71   7.317%   $254.0301   $254.03   $254.05   $254.00  
  Purchase #5 $198.46   8.277%   $214.8865   $214.89   $214.90   $214.90  
  Purchase #6 $117.30   12.374%   $131.8147   $131.81   $131.80   $131.80  
  Purchase #7 $209.53   12.725%   $236.1927   $236.19   $236.20   $236.20  
  7 purchase totals = $1,151.00       $1,246.1155   $1,246.12   $1,246.15   $1,246.10