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 $64.93   6.783%   $69.3342   $69.33   $69.35   $69.30  
  Purchase #2 $218.44   6.195%   $231.9724   $231.97   $231.95   $232.00  
  Purchase #3 $148.73   9.216%   $162.437   $162.44   $162.45   $162.40  
  Purchase #4 $37.88   6.154%   $40.2111   $40.21   $40.20   $40.20  
  Purchase #5 $101.89   13.497%   $115.6421   $115.64   $115.65   $115.60  
  Purchase #6 $69.95   5.703%   $73.9392   $73.94   $73.95   $73.90  
  Purchase #7 $98.80   13.355%   $111.9947   $111.99   $112.00   $112.00  
  7 purchase totals = $740.62       $805.5307   $805.52   $805.55   $805.40