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 $53.76   10.312%   $59.3037   $59.30   $59.30   $59.30  
  Purchase #2 $204.33   12.378%   $229.622   $229.62   $229.60   $229.60  
  Purchase #3 $139.59   5.334%   $147.0357   $147.04   $147.05   $147.00  
  Purchase #4 $5.68   10.125%   $6.2551   $6.26   $6.25   $6.30  
  Purchase #5 $191.51   5.104%   $201.2847   $201.28   $201.30   $201.30  
  Purchase #6 $131.62   7.144%   $141.0229   $141.02   $141.00   $141.00  
  Purchase #7 $226.64   4.788%   $237.4915   $237.49   $237.50   $237.50  
  7 purchase totals = $953.13       $1,022.0156   $1,022.01   $1,022.00   $1,022.00