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 $93.30   8.535%   $101.2632   $101.26   $101.25   $101.30  
  Purchase #2 $237.74   12.607%   $267.7119   $267.71   $267.70   $267.70  
  Purchase #3 $6.82   4.527%   $7.1287   $7.13   $7.15   $7.10  
  Purchase #4 $206.34   5.439%   $217.5628   $217.56   $217.55   $217.60  
  Purchase #5 $113.34   6.718%   $120.9542   $120.95   $120.95   $121.00  
  Purchase #6 $180.54   13.265%   $204.4886   $204.49   $204.50   $204.50  
  Purchase #7 $125.47   12.437%   $141.0747   $141.07   $141.05   $141.10  
  7 purchase totals = $963.55       $1,060.1841   $1,060.17   $1,060.15   $1,060.30