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 $152.45   13.807%   $173.4988   $173.50   $173.50   $173.50  
  Purchase #2 $77.93   12.121%   $87.3759   $87.38   $87.40   $87.40  
  Purchase #3 $136.51   9.627%   $149.6518   $149.65   $149.65   $149.70  
  Purchase #4 $96.82   4.813%   $101.4799   $101.48   $101.50   $101.50  
  Purchase #5 $51.34   5.717%   $54.2751   $54.28   $54.30   $54.30  
  Purchase #6 $232.53   3.528%   $240.7337   $240.73   $240.75   $240.70  
  Purchase #7 $188.96   9.538%   $206.983   $206.98   $207.00   $207.00  
  7 purchase totals = $936.54       $1,013.9982   $1,014.00   $1,014.10   $1,014.10