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 $188.95   6.614%   $201.4472   $201.45   $201.45   $201.40  
  Purchase #2 $145.89   12.123%   $163.5762   $163.58   $163.60   $163.60  
  Purchase #3 $103.71   4.849%   $108.7389   $108.74   $108.75   $108.70  
  Purchase #4 $141.62   12.537%   $159.3749   $159.37   $159.35   $159.40  
  Purchase #5 $108.87   5.854%   $115.2432   $115.24   $115.25   $115.20  
  Purchase #6 $237.38   10.646%   $262.6515   $262.65   $262.65   $262.70  
  Purchase #7 $137.88   7.545%   $148.283   $148.28   $148.30   $148.30  
  7 purchase totals = $1,064.30       $1,159.3149   $1,159.31   $1,159.35   $1,159.30