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 $61.74   10.539%   $68.2468   $68.25   $68.25   $68.20  
  Purchase #2 $148.82   6.532%   $158.5409   $158.54   $158.55   $158.50  
  Purchase #3 $10.93   7.709%   $11.7726   $11.77   $11.75   $11.80  
  Purchase #4 $192.83   4.450%   $201.4109   $201.41   $201.40   $201.40  
  Purchase #5 $96.59   8.230%   $104.5394   $104.54   $104.55   $104.50  
  Purchase #6 $88.62   12.665%   $99.8437   $99.84   $99.85   $99.80  
  Purchase #7 $62.31   12.398%   $70.0352   $70.04   $70.05   $70.00  
  7 purchase totals = $661.84       $714.3895   $714.39   $714.40   $714.20