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 $56.66   8.839%   $61.6682   $61.67   $61.65   $61.70  
  Purchase #2 $136.59   7.346%   $146.6239   $146.62   $146.60   $146.60  
  Purchase #3 $56.75   8.463%   $61.5528   $61.55   $61.55   $61.60  
  Purchase #4 $168.58   12.548%   $189.7334   $189.73   $189.75   $189.70  
  Purchase #5 $237.26   12.589%   $267.1287   $267.13   $267.15   $267.10  
  Purchase #6 $189.85   10.620%   $210.0121   $210.01   $210.00   $210.00  
  Purchase #7 $104.33   4.429%   $108.9508   $108.95   $108.95   $109.00  
  7 purchase totals = $950.02       $1,045.6699   $1,045.66   $1,045.65   $1,045.70