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 $73.44   5.669%   $77.6033   $77.60   $77.60   $77.60  
  Purchase #2 $95.25   9.835%   $104.6178   $104.62   $104.60   $104.60  
  Purchase #3 $204.72   7.547%   $220.1702   $220.17   $220.15   $220.20  
  Purchase #4 $200.30   7.170%   $214.6615   $214.66   $214.65   $214.70  
  Purchase #5 $64.97   12.425%   $73.0425   $73.04   $73.05   $73.00  
  Purchase #6 $24.38   3.310%   $25.187   $25.19   $25.20   $25.20  
  Purchase #7 $235.39   6.530%   $250.761   $250.76   $250.75   $250.80  
  7 purchase totals = $898.45       $966.0433   $966.04   $966.00   $966.10