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 $152.73   12.756%   $172.2122   $172.21   $172.20   $172.20  
  Purchase #2 $119.57   5.362%   $125.9813   $125.98   $126.00   $126.00  
  Purchase #3 $203.80   7.412%   $218.9057   $218.91   $218.90   $218.90  
  Purchase #4 $63.97   11.157%   $71.1071   $71.11   $71.10   $71.10  
  Purchase #5 $88.29   11.294%   $98.2615   $98.26   $98.25   $98.30  
  Purchase #6 $127.83   4.732%   $133.8789   $133.88   $133.90   $133.90  
  Purchase #7 $181.94   12.370%   $204.446   $204.45   $204.45   $204.40  
  7 purchase totals = $938.13       $1,024.7927   $1,024.80   $1,024.80   $1,024.80