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 $125.51   11.824%   $140.3503   $140.35   $140.35   $140.40  
  Purchase #2 $197.26   5.269%   $207.6536   $207.65   $207.65   $207.70  
  Purchase #3 $11.91   6.441%   $12.6771   $12.68   $12.70   $12.70  
  Purchase #4 $240.55   8.293%   $260.4988   $260.50   $260.50   $260.50  
  Purchase #5 $147.80   4.725%   $154.7836   $154.78   $154.80   $154.80  
  Purchase #6 $207.97   7.242%   $223.0312   $223.03   $223.05   $223.00  
  Purchase #7 $57.37   4.313%   $59.8444   $59.84   $59.85   $59.80  
  7 purchase totals = $988.37       $1,058.8390   $1,058.83   $1,058.90   $1,058.90