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 $135.64   8.345%   $146.9592   $146.96   $146.95   $147.00  
  Purchase #2 $131.46   13.803%   $149.6054   $149.61   $149.60   $149.60  
  Purchase #3 $124.87   9.509%   $136.7439   $136.74   $136.75   $136.70  
  Purchase #4 $101.73   5.670%   $107.4981   $107.50   $107.50   $107.50  
  Purchase #5 $39.80   3.157%   $41.0565   $41.06   $41.05   $41.10  
  Purchase #6 $229.34   9.643%   $251.4553   $251.46   $251.45   $251.50  
  Purchase #7 $174.80   9.617%   $191.6105   $191.61   $191.60   $191.60  
  7 purchase totals = $937.64       $1,024.9289   $1,024.94   $1,024.90   $1,025.00