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 $50.73   5.152%   $53.3436   $53.34   $53.35   $53.30  
  Purchase #2 $250.91   10.384%   $276.9645   $276.96   $276.95   $277.00  
  Purchase #3 $16.70   10.374%   $18.4325   $18.43   $18.45   $18.40  
  Purchase #4 $250.26   6.857%   $267.4203   $267.42   $267.40   $267.40  
  Purchase #5 $122.86   5.501%   $129.6185   $129.62   $129.60   $129.60  
  Purchase #6 $235.80   4.344%   $246.0432   $246.04   $246.05   $246.00  
  Purchase #7 $146.75   6.716%   $156.6057   $156.61   $156.60   $156.60  
  7 purchase totals = $1,074.01       $1,148.4283   $1,148.42   $1,148.40   $1,148.30