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 $235.53   5.532%   $248.5595   $248.56   $248.55   $248.60  
  Purchase #2 $93.91   4.227%   $97.8796   $97.88   $97.90   $97.90  
  Purchase #3 $201.68   5.675%   $213.1253   $213.13   $213.15   $213.10  
  Purchase #4 $8.34   6.819%   $8.9087   $8.91   $8.90   $8.90  
  Purchase #5 $147.80   8.128%   $159.8132   $159.81   $159.80   $159.80  
  Purchase #6 $81.98   12.181%   $91.966   $91.97   $91.95   $92.00  
  Purchase #7 $191.61   4.587%   $200.3992   $200.40   $200.40   $200.40  
  7 purchase totals = $960.85       $1,020.6515   $1,020.66   $1,020.65   $1,020.70