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 $179.59   6.856%   $191.9027   $191.90   $191.90   $191.90  
  Purchase #2 $79.85   10.458%   $88.2007   $88.20   $88.20   $88.20  
  Purchase #3 $59.60   5.281%   $62.7475   $62.75   $62.75   $62.70  
  Purchase #4 $201.27   6.269%   $213.8876   $213.89   $213.90   $213.90  
  Purchase #5 $99.90   13.496%   $113.3825   $113.38   $113.40   $113.40  
  Purchase #6 $126.97   6.554%   $135.2916   $135.29   $135.30   $135.30  
  Purchase #7 $232.43   3.395%   $240.321   $240.32   $240.30   $240.30  
  7 purchase totals = $979.61       $1,045.7336   $1,045.73   $1,045.75   $1,045.70