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 $115.36   8.614%   $125.2971   $125.30   $125.30   $125.30  
  Purchase #2 $153.42   4.245%   $159.9327   $159.93   $159.95   $159.90  
  Purchase #3 $246.71   9.160%   $269.3086   $269.31   $269.30   $269.30  
  Purchase #4 $111.97   6.541%   $119.294   $119.29   $119.30   $119.30  
  Purchase #5 $190.88   13.169%   $216.017   $216.02   $216.00   $216.00  
  Purchase #6 $105.88   11.752%   $118.323   $118.32   $118.30   $118.30  
  Purchase #7 $150.89   12.112%   $169.1658   $169.17   $169.15   $169.20  
  7 purchase totals = $1,075.11       $1,177.3382   $1,177.34   $1,177.30   $1,177.30