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 $244.66   13.203%   $276.9625   $276.96   $276.95   $277.00  
  Purchase #2 $187.25   13.572%   $212.6636   $212.66   $212.65   $212.70  
  Purchase #3 $93.80   4.360%   $97.8897   $97.89   $97.90   $97.90  
  Purchase #4 $130.67   9.679%   $143.3175   $143.32   $143.30   $143.30  
  Purchase #5 $48.70   5.745%   $51.4978   $51.50   $51.50   $51.50  
  Purchase #6 $184.72   6.333%   $196.4183   $196.42   $196.40   $196.40  
  Purchase #7 $47.97   8.468%   $52.0321   $52.03   $52.05   $52.00  
  7 purchase totals = $937.77       $1,030.7815   $1,030.78   $1,030.75   $1,030.80