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 $53.48   13.560%   $60.7319   $60.73   $60.75   $60.70  
  Purchase #2 $169.66   7.531%   $182.4371   $182.44   $182.45   $182.40  
  Purchase #3 $56.59   4.428%   $59.0958   $59.10   $59.10   $59.10  
  Purchase #4 $191.54   10.545%   $211.7379   $211.74   $211.75   $211.70  
  Purchase #5 $156.87   12.126%   $175.8921   $175.89   $175.90   $175.90  
  Purchase #6 $204.58   13.230%   $231.6459   $231.65   $231.65   $231.60  
  Purchase #7 $101.98   4.532%   $106.6017   $106.60   $106.60   $106.60  
  7 purchase totals = $934.70       $1,028.1424   $1,028.15   $1,028.20   $1,028.00