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 $179.28   13.499%   $203.481   $203.48   $203.50   $203.50  
  Purchase #2 $112.81   11.340%   $125.6027   $125.60   $125.60   $125.60  
  Purchase #3 $23.66   13.289%   $26.8042   $26.80   $26.80   $26.80  
  Purchase #4 $182.43   11.705%   $203.7834   $203.78   $203.80   $203.80  
  Purchase #5 $73.98   11.329%   $82.3612   $82.36   $82.35   $82.40  
  Purchase #6 $47.95   9.666%   $52.5848   $52.58   $52.60   $52.60  
  Purchase #7 $231.92   3.130%   $239.1791   $239.18   $239.20   $239.20  
  7 purchase totals = $852.03       $933.7964   $933.78   $933.85   $933.90