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 $32.95   4.278%   $34.3596   $34.36   $34.35   $34.40  
  Purchase #2 $87.32   8.757%   $94.9666   $94.97   $94.95   $95.00  
  Purchase #3 $25.49   6.238%   $27.0801   $27.08   $27.10   $27.10  
  Purchase #4 $169.92   13.866%   $193.4811   $193.48   $193.50   $193.50  
  Purchase #5 $180.63   4.852%   $189.3942   $189.39   $189.40   $189.40  
  Purchase #6 $218.64   6.594%   $233.0571   $233.06   $233.05   $233.10  
  Purchase #7 $120.70   3.584%   $125.0259   $125.03   $125.05   $125.00  
  7 purchase totals = $835.65       $897.3646   $897.37   $897.40   $897.50