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 $246.59   8.588%   $267.7671   $267.77   $267.75   $267.80  
  Purchase #2 $68.81   5.793%   $72.7962   $72.80   $72.80   $72.80  
  Purchase #3 $95.81   9.116%   $104.544   $104.54   $104.55   $104.50  
  Purchase #4 $141.36   13.304%   $160.1665   $160.17   $160.15   $160.20  
  Purchase #5 $97.37   7.257%   $104.4361   $104.44   $104.45   $104.40  
  Purchase #6 $190.71   6.758%   $203.5982   $203.60   $203.60   $203.60  
  Purchase #7 $103.35   4.545%   $108.0473   $108.05   $108.05   $108.00  
  7 purchase totals = $944.00       $1,021.3554   $1,021.37   $1,021.35   $1,021.30