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 $28.26   8.121%   $30.555   $30.56   $30.55   $30.60  
  Purchase #2 $250.95   5.636%   $265.0935   $265.09   $265.10   $265.10  
  Purchase #3 $88.44   6.511%   $94.1983   $94.20   $94.20   $94.20  
  Purchase #4 $19.81   3.765%   $20.5558   $20.56   $20.55   $20.60  
  Purchase #5 $132.93   10.319%   $146.647   $146.65   $146.65   $146.60  
  Purchase #6 $232.56   7.761%   $250.609   $250.61   $250.60   $250.60  
  Purchase #7 $215.34   5.182%   $226.4989   $226.50   $226.50   $226.50  
  7 purchase totals = $968.29       $1,034.1575   $1,034.17   $1,034.15   $1,034.20