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 $61.82   12.311%   $69.4307   $69.43   $69.45   $69.40  
  Purchase #2 $132.84   8.558%   $144.2084   $144.21   $144.20   $144.20  
  Purchase #3 $71.75   3.216%   $74.0575   $74.06   $74.05   $74.10  
  Purchase #4 $120.91   9.309%   $132.1655   $132.17   $132.15   $132.20  
  Purchase #5 $242.84   3.720%   $251.8736   $251.87   $251.85   $251.90  
  Purchase #6 $21.43   7.515%   $23.0405   $23.04   $23.05   $23.00  
  Purchase #7 $93.37   6.301%   $99.2532   $99.25   $99.25   $99.30  
  7 purchase totals = $744.96       $794.0294   $794.03   $794.00   $794.10