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 $148.84   13.722%   $169.2638   $169.26   $169.25   $169.30  
  Purchase #2 $66.64   10.141%   $73.398   $73.40   $73.40   $73.40  
  Purchase #3 $176.54   11.285%   $196.4625   $196.46   $196.45   $196.50  
  Purchase #4 $195.87   5.352%   $206.353   $206.35   $206.35   $206.40  
  Purchase #5 $100.64   9.797%   $110.4997   $110.50   $110.50   $110.50  
  Purchase #6 $213.59   12.342%   $239.9513   $239.95   $239.95   $240.00  
  Purchase #7 $131.68   11.478%   $146.7942   $146.79   $146.80   $146.80  
  7 purchase totals = $1,033.80       $1,142.7225   $1,142.71   $1,142.70   $1,142.90