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 $85.28   12.803%   $96.1984   $96.20   $96.20   $96.20  
  Purchase #2 $233.86   3.610%   $242.3023   $242.30   $242.30   $242.30  
  Purchase #3 $137.96   6.777%   $147.3095   $147.31   $147.30   $147.30  
  Purchase #4 $150.34   13.489%   $170.6194   $170.62   $170.60   $170.60  
  Purchase #5 $69.92   9.358%   $76.4631   $76.46   $76.45   $76.50  
  Purchase #6 $84.66   8.724%   $92.0457   $92.05   $92.05   $92.00  
  Purchase #7 $178.46   3.545%   $184.7864   $184.79   $184.80   $184.80  
  7 purchase totals = $940.48       $1,009.7248   $1,009.73   $1,009.70   $1,009.70