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 $76.42   12.379%   $85.88   $85.88   $85.90   $85.90  
  Purchase #2 $125.63   7.617%   $135.1992   $135.20   $135.20   $135.20  
  Purchase #3 $163.38   11.240%   $181.7439   $181.74   $181.75   $181.70  
  Purchase #4 $91.40   4.340%   $95.3668   $95.37   $95.35   $95.40  
  Purchase #5 $116.48   7.726%   $125.4792   $125.48   $125.50   $125.50  
  Purchase #6 $216.61   11.278%   $241.0393   $241.04   $241.05   $241.00  
  Purchase #7 $184.56   5.842%   $195.342   $195.34   $195.35   $195.30  
  7 purchase totals = $974.48       $1,060.0504   $1,060.05   $1,060.10   $1,060.00