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 $246.38   8.438%   $267.1695   $267.17   $267.15   $267.20  
  Purchase #2 $215.26   13.179%   $243.6291   $243.63   $243.65   $243.60  
  Purchase #3 $74.43   9.736%   $81.6765   $81.68   $81.70   $81.70  
  Purchase #4 $156.90   4.764%   $164.3747   $164.37   $164.35   $164.40  
  Purchase #5 $208.73   4.754%   $218.653   $218.65   $218.65   $218.70  
  Purchase #6 $143.96   12.720%   $162.2717   $162.27   $162.25   $162.30  
  Purchase #7 $131.75   4.729%   $137.9805   $137.98   $138.00   $138.00  
  7 purchase totals = $1,177.41       $1,275.7550   $1,275.75   $1,275.75   $1,275.90