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 $64.85   13.266%   $73.453   $73.45   $73.45   $73.50  
  Purchase #2 $123.67   8.617%   $134.3266   $134.33   $134.35   $134.30  
  Purchase #3 $61.66   4.200%   $64.2497   $64.25   $64.25   $64.20  
  Purchase #4 $59.32   9.142%   $64.743   $64.74   $64.75   $64.70  
  Purchase #5 $174.57   5.701%   $184.5222   $184.52   $184.50   $184.50  
  Purchase #6 $184.83   12.572%   $208.0668   $208.07   $208.05   $208.10  
  Purchase #7 $198.57   4.562%   $207.6288   $207.63   $207.65   $207.60  
  7 purchase totals = $867.47       $936.9901   $936.99   $937.00   $936.90