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 $227.75   10.597%   $251.8847   $251.88   $251.90   $251.90  
  Purchase #2 $167.40   6.628%   $178.4953   $178.50   $178.50   $178.50  
  Purchase #3 $49.65   8.200%   $53.7213   $53.72   $53.70   $53.70  
  Purchase #4 $93.42   6.468%   $99.4624   $99.46   $99.45   $99.50  
  Purchase #5 $201.27   5.141%   $211.6173   $211.62   $211.60   $211.60  
  Purchase #6 $141.30   11.555%   $157.6272   $157.63   $157.65   $157.60  
  Purchase #7 $177.45   9.601%   $194.487   $194.49   $194.50   $194.50  
  7 purchase totals = $1,058.24       $1,147.2952   $1,147.30   $1,147.30   $1,147.30