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 $180.31   12.855%   $203.4889   $203.49   $203.50   $203.50  
  Purchase #2 $203.84   6.656%   $217.4076   $217.41   $217.40   $217.40  
  Purchase #3 $67.65   4.621%   $70.7761   $70.78   $70.80   $70.80  
  Purchase #4 $30.75   13.364%   $34.8594   $34.86   $34.85   $34.90  
  Purchase #5 $95.81   4.260%   $99.8915   $99.89   $99.90   $99.90  
  Purchase #6 $159.28   7.669%   $171.4952   $171.50   $171.50   $171.50  
  Purchase #7 $216.60   8.371%   $234.7316   $234.73   $234.75   $234.70  
  7 purchase totals = $954.24       $1,032.6503   $1,032.66   $1,032.70   $1,032.70