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 $96.73   7.804%   $104.2788   $104.28   $104.30   $104.30  
  Purchase #2 $55.49   12.387%   $62.3635   $62.36   $62.35   $62.40  
  Purchase #3 $141.68   4.290%   $147.7581   $147.76   $147.75   $147.80  
  Purchase #4 $83.81   13.812%   $95.3858   $95.39   $95.40   $95.40  
  Purchase #5 $66.92   5.499%   $70.5999   $70.60   $70.60   $70.60  
  Purchase #6 $198.47   7.171%   $212.7023   $212.70   $212.70   $212.70  
  Purchase #7 $243.89   3.190%   $251.6701   $251.67   $251.65   $251.70  
  7 purchase totals = $886.99       $944.7585   $944.76   $944.75   $944.90