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 $237.96   11.373%   $265.0232   $265.02   $265.00   $265.00  
  Purchase #2 $203.93   9.374%   $223.0464   $223.05   $223.05   $223.00  
  Purchase #3 $156.50   12.366%   $175.8528   $175.85   $175.85   $175.90  
  Purchase #4 $55.70   8.173%   $60.2524   $60.25   $60.25   $60.30  
  Purchase #5 $83.84   12.470%   $94.2948   $94.29   $94.30   $94.30  
  Purchase #6 $205.93   6.159%   $218.6132   $218.61   $218.60   $218.60  
  Purchase #7 $136.32   3.730%   $141.4047   $141.40   $141.40   $141.40  
  7 purchase totals = $1,080.18       $1,178.4875   $1,178.47   $1,178.45   $1,178.50