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 $199.70   9.106%   $217.8847   $217.88   $217.90   $217.90  
  Purchase #2 $178.91   6.586%   $190.693   $190.69   $190.70   $190.70  
  Purchase #3 $177.87   6.628%   $189.6592   $189.66   $189.65   $189.70  
  Purchase #4 $176.63   4.627%   $184.8027   $184.80   $184.80   $184.80  
  Purchase #5 $73.78   9.345%   $80.6747   $80.67   $80.65   $80.70  
  Purchase #6 $6.95   11.373%   $7.7404   $7.74   $7.75   $7.70  
  Purchase #7 $130.54   6.379%   $138.8671   $138.87   $138.85   $138.90  
  7 purchase totals = $944.38       $1,010.3218   $1,010.31   $1,010.30   $1,010.40