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 $130.74   13.806%   $148.79   $148.79   $148.80   $148.80  
  Purchase #2 $93.99   13.384%   $106.5696   $106.57   $106.55   $106.60  
  Purchase #3 $189.52   7.112%   $202.9987   $203.00   $203.00   $203.00  
  Purchase #4 $148.68   9.154%   $162.2902   $162.29   $162.30   $162.30  
  Purchase #5 $231.39   7.598%   $248.971   $248.97   $248.95   $249.00  
  Purchase #6 $12.67   12.629%   $14.2701   $14.27   $14.25   $14.30  
  Purchase #7 $168.96   8.622%   $183.5277   $183.53   $183.55   $183.50  
  7 purchase totals = $975.95       $1,067.4173   $1,067.42   $1,067.40   $1,067.50