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 $206.67   13.597%   $234.7709   $234.77   $234.75   $234.80  
  Purchase #2 $172.72   11.379%   $192.3738   $192.37   $192.35   $192.40  
  Purchase #3 $216.87   12.751%   $244.5231   $244.52   $244.50   $244.50  
  Purchase #4 $60.86   4.323%   $63.491   $63.49   $63.50   $63.50  
  Purchase #5 $106.79   8.359%   $115.7166   $115.72   $115.70   $115.70  
  Purchase #6 $125.64   8.863%   $136.7755   $136.78   $136.80   $136.80  
  Purchase #7 $67.71   10.341%   $74.7119   $74.71   $74.70   $74.70  
  7 purchase totals = $957.26       $1,062.3628   $1,062.36   $1,062.30   $1,062.40