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 $47.87   8.638%   $52.005   $52.01   $52.00   $52.00  
  Purchase #2 $119.97   9.364%   $131.204   $131.20   $131.20   $131.20  
  Purchase #3 $218.98   11.654%   $244.4999   $244.50   $244.50   $244.50  
  Purchase #4 $213.77   7.790%   $230.4227   $230.42   $230.40   $230.40  
  Purchase #5 $50.75   6.181%   $53.8869   $53.89   $53.90   $53.90  
  Purchase #6 $235.42   9.814%   $258.5241   $258.52   $258.50   $258.50  
  Purchase #7 $62.69   10.519%   $69.2844   $69.28   $69.30   $69.30  
  7 purchase totals = $949.45       $1,039.8270   $1,039.82   $1,039.80   $1,039.80