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 $33.46   7.790%   $36.0665   $36.07   $36.05   $36.10  
  Purchase #2 $157.72   11.860%   $176.4256   $176.43   $176.45   $176.40  
  Purchase #3 $6.54   13.410%   $7.417   $7.42   $7.40   $7.40  
  Purchase #4 $225.68   8.345%   $244.513   $244.51   $244.50   $244.50  
  Purchase #5 $52.42   9.421%   $57.3585   $57.36   $57.35   $57.40  
  Purchase #6 $195.53   9.374%   $213.859   $213.86   $213.85   $213.90  
  Purchase #7 $161.33   8.676%   $175.327   $175.33   $175.35   $175.30  
  7 purchase totals = $832.68       $910.9666   $910.98   $910.95   $911.00