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 $172.87   12.570%   $194.5998   $194.60   $194.60   $194.60  
  Purchase #2 $226.86   5.334%   $238.9607   $238.96   $238.95   $239.00  
  Purchase #3 $49.29   9.454%   $53.9499   $53.95   $53.95   $53.90  
  Purchase #4 $66.70   12.175%   $74.8207   $74.82   $74.80   $74.80  
  Purchase #5 $50.63   9.397%   $55.3877   $55.39   $55.40   $55.40  
  Purchase #6 $223.46   3.127%   $230.4476   $230.45   $230.45   $230.40  
  Purchase #7 $208.46   4.114%   $217.036   $217.04   $217.05   $217.00  
  7 purchase totals = $998.27       $1,065.2024   $1,065.21   $1,065.20   $1,065.10