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 $206.47   12.860%   $233.022   $233.02   $233.00   $233.00  
  Purchase #2 $99.77   8.197%   $107.9481   $107.95   $107.95   $107.90  
  Purchase #3 $32.69   8.698%   $35.5334   $35.53   $35.55   $35.50  
  Purchase #4 $52.48   8.163%   $56.7639   $56.76   $56.75   $56.80  
  Purchase #5 $206.83   9.651%   $226.7912   $226.79   $226.80   $226.80  
  Purchase #6 $40.42   3.362%   $41.7789   $41.78   $41.80   $41.80  
  Purchase #7 $204.65   3.853%   $212.5352   $212.54   $212.55   $212.50  
  7 purchase totals = $843.31       $914.3727   $914.37   $914.40   $914.30