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 $30.46   7.616%   $32.7798   $32.78   $32.80   $32.80  
  Purchase #2 $214.96   10.696%   $237.9521   $237.95   $237.95   $238.00  
  Purchase #3 $160.54   5.330%   $169.0968   $169.10   $169.10   $169.10  
  Purchase #4 $169.79   10.679%   $187.9219   $187.92   $187.90   $187.90  
  Purchase #5 $73.56   3.159%   $75.8838   $75.88   $75.90   $75.90  
  Purchase #6 $132.79   4.255%   $138.4402   $138.44   $138.45   $138.40  
  Purchase #7 $55.68   12.437%   $62.6049   $62.60   $62.60   $62.60  
  7 purchase totals = $837.78       $904.6795   $904.67   $904.70   $904.70