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 $107.40   7.835%   $115.8148   $115.81   $115.80   $115.80  
  Purchase #2 $145.84   3.405%   $150.8059   $150.81   $150.80   $150.80  
  Purchase #3 $27.94   6.220%   $29.6779   $29.68   $29.70   $29.70  
  Purchase #4 $148.40   8.235%   $160.6207   $160.62   $160.60   $160.60  
  Purchase #5 $70.26   3.191%   $72.502   $72.50   $72.50   $72.50  
  Purchase #6 $62.75   6.428%   $66.7836   $66.78   $66.80   $66.80  
  Purchase #7 $125.75   10.486%   $138.9361   $138.94   $138.95   $138.90  
  7 purchase totals = $688.34       $735.1410   $735.14   $735.15   $735.10