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 $213.56   5.862%   $226.0789   $226.08   $226.10   $226.10  
  Purchase #2 $230.94   7.720%   $248.7686   $248.77   $248.75   $248.80  
  Purchase #3 $167.99   6.139%   $178.3029   $178.30   $178.30   $178.30  
  Purchase #4 $91.87   6.342%   $97.6964   $97.70   $97.70   $97.70  
  Purchase #5 $208.73   4.713%   $218.5674   $218.57   $218.55   $218.60  
  Purchase #6 $61.50   10.573%   $68.0024   $68.00   $68.00   $68.00  
  Purchase #7 $23.97   9.168%   $26.1676   $26.17   $26.15   $26.20  
  7 purchase totals = $998.56       $1,063.5842   $1,063.59   $1,063.55   $1,063.70