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 $204.98   10.373%   $226.2426   $226.24   $226.25   $226.20  
  Purchase #2 $174.56   13.557%   $198.2251   $198.23   $198.25   $198.20  
  Purchase #3 $100.84   4.191%   $105.0662   $105.07   $105.05   $105.10  
  Purchase #4 $41.79   4.561%   $43.696   $43.70   $43.70   $43.70  
  Purchase #5 $178.70   8.766%   $194.3648   $194.36   $194.35   $194.40  
  Purchase #6 $11.50   3.804%   $11.9375   $11.94   $11.95   $11.90  
  Purchase #7 $193.32   13.400%   $219.2249   $219.22   $219.20   $219.20  
  7 purchase totals = $905.69       $998.7571   $998.76   $998.75   $998.70