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 $41.84   11.846%   $46.7964   $46.80   $46.80   $46.80  
  Purchase #2 $53.41   12.852%   $60.2743   $60.27   $60.25   $60.30  
  Purchase #3 $133.54   12.752%   $150.569   $150.57   $150.55   $150.60  
  Purchase #4 $59.73   5.179%   $62.8234   $62.82   $62.80   $62.80  
  Purchase #5 $175.77   6.543%   $187.2706   $187.27   $187.25   $187.30  
  Purchase #6 $115.93   5.597%   $122.4186   $122.42   $122.40   $122.40  
  Purchase #7 $159.61   3.707%   $165.5267   $165.53   $165.55   $165.50  
  7 purchase totals = $739.83       $795.6790   $795.68   $795.60   $795.70