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 $176.51   4.691%   $184.7901   $184.79   $184.80   $184.80  
  Purchase #2 $88.85   12.211%   $99.6995   $99.70   $99.70   $99.70  
  Purchase #3 $38.48   8.272%   $41.6631   $41.66   $41.65   $41.70  
  Purchase #4 $51.54   13.136%   $58.3103   $58.31   $58.30   $58.30  
  Purchase #5 $126.96   8.506%   $137.7592   $137.76   $137.75   $137.80  
  Purchase #6 $69.31   7.874%   $74.7675   $74.77   $74.75   $74.80  
  Purchase #7 $146.41   13.192%   $165.7244   $165.72   $165.70   $165.70  
  7 purchase totals = $698.06       $762.7141   $762.71   $762.65   $762.80