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 $198.88   6.359%   $211.5268   $211.53   $211.55   $211.50  
  Purchase #2 $103.68   3.160%   $106.9563   $106.96   $106.95   $107.00  
  Purchase #3 $22.31   4.279%   $23.2646   $23.26   $23.25   $23.30  
  Purchase #4 $239.30   13.133%   $270.7273   $270.73   $270.75   $270.70  
  Purchase #5 $170.89   6.795%   $182.502   $182.50   $182.50   $182.50  
  Purchase #6 $57.53   12.196%   $64.5464   $64.55   $64.55   $64.50  
  Purchase #7 $164.91   6.136%   $175.0289   $175.03   $175.05   $175.00  
  7 purchase totals = $957.50       $1,034.5523   $1,034.56   $1,034.60   $1,034.50