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 $183.65   10.676%   $203.2565   $203.26   $203.25   $203.30  
  Purchase #2 $245.59   12.376%   $275.9842   $275.98   $276.00   $276.00  
  Purchase #3 $5.51   7.582%   $5.9278   $5.93   $5.95   $5.90  
  Purchase #4 $144.34   6.387%   $153.559   $153.56   $153.55   $153.60  
  Purchase #5 $98.89   8.206%   $107.0049   $107.00   $107.00   $107.00  
  Purchase #6 $56.84   13.478%   $64.5009   $64.50   $64.50   $64.50  
  Purchase #7 $127.25   13.800%   $144.8105   $144.81   $144.80   $144.80  
  7 purchase totals = $862.07       $955.0438   $955.04   $955.05   $955.10