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 $82.67   13.816%   $94.0917   $94.09   $94.10   $94.10  
  Purchase #2 $191.91   6.769%   $204.9004   $204.90   $204.90   $204.90  
  Purchase #3 $91.40   3.458%   $94.5606   $94.56   $94.55   $94.60  
  Purchase #4 $245.99   12.860%   $277.6243   $277.62   $277.60   $277.60  
  Purchase #5 $125.42   13.531%   $142.3906   $142.39   $142.40   $142.40  
  Purchase #6 $206.69   8.851%   $224.9841   $224.98   $225.00   $225.00  
  Purchase #7 $200.99   7.469%   $216.0019   $216.00   $216.00   $216.00  
  7 purchase totals = $1,145.07       $1,254.5536   $1,254.54   $1,254.55   $1,254.60