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 $5.37   12.195%   $6.0249   $6.02   $6.00   $6.00  
  Purchase #2 $113.89   11.298%   $126.7573   $126.76   $126.75   $126.80  
  Purchase #3 $92.78   8.170%   $100.3601   $100.36   $100.35   $100.40  
  Purchase #4 $61.40   5.572%   $64.8212   $64.82   $64.80   $64.80  
  Purchase #5 $184.51   11.373%   $205.4943   $205.49   $205.50   $205.50  
  Purchase #6 $194.93   7.577%   $209.6998   $209.70   $209.70   $209.70  
  Purchase #7 $137.47   3.664%   $142.5069   $142.51   $142.50   $142.50  
  7 purchase totals = $790.35       $855.6645   $855.66   $855.60   $855.70