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 $204.66   13.797%   $232.8969   $232.90   $232.90   $232.90  
  Purchase #2 $249.93   5.129%   $262.7489   $262.75   $262.75   $262.70  
  Purchase #3 $72.26   7.296%   $77.5321   $77.53   $77.55   $77.50  
  Purchase #4 $65.79   6.507%   $70.071   $70.07   $70.05   $70.10  
  Purchase #5 $243.58   9.593%   $266.9466   $266.95   $266.95   $266.90  
  Purchase #6 $131.92   13.271%   $149.4271   $149.43   $149.45   $149.40  
  Purchase #7 $20.89   9.289%   $22.8305   $22.83   $22.85   $22.80  
  7 purchase totals = $989.03       $1,082.4531   $1,082.46   $1,082.50   $1,082.30