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 $108.89   8.619%   $118.2752   $118.28   $118.30   $118.30  
  Purchase #2 $153.62   10.672%   $170.0143   $170.01   $170.00   $170.00  
  Purchase #3 $250.54   8.335%   $271.4225   $271.42   $271.40   $271.40  
  Purchase #4 $216.72   6.593%   $231.0083   $231.01   $231.00   $231.00  
  Purchase #5 $52.53   12.363%   $59.0243   $59.02   $59.00   $59.00  
  Purchase #6 $213.90   8.342%   $231.7435   $231.74   $231.75   $231.70  
  Purchase #7 $166.89   3.744%   $173.1384   $173.14   $173.15   $173.10  
  7 purchase totals = $1,163.09       $1,254.6265   $1,254.62   $1,254.60   $1,254.50