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 $205.79   13.465%   $233.4996   $233.50   $233.50   $233.50  
  Purchase #2 $232.41   5.193%   $244.4791   $244.48   $244.50   $244.50  
  Purchase #3 $115.84   7.421%   $124.4365   $124.44   $124.45   $124.40  
  Purchase #4 $5.96   12.200%   $6.6871   $6.69   $6.70   $6.70  
  Purchase #5 $150.75   11.793%   $168.5279   $168.53   $168.55   $168.50  
  Purchase #6 $240.73   5.140%   $253.1035   $253.10   $253.10   $253.10  
  Purchase #7 $218.72   12.594%   $246.2656   $246.27   $246.25   $246.30  
  7 purchase totals = $1,170.20       $1,276.9993   $1,277.01   $1,277.05   $1,277.00