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 $185.86   3.842%   $193.0007   $193.00   $193.00   $193.00  
  Purchase #2 $171.39   13.863%   $195.1498   $195.15   $195.15   $195.10  
  Purchase #3 $174.92   9.355%   $191.2838   $191.28   $191.30   $191.30  
  Purchase #4 $158.32   5.696%   $167.3379   $167.34   $167.35   $167.30  
  Purchase #5 $85.81   11.397%   $95.5898   $95.59   $95.60   $95.60  
  Purchase #6 $86.76   11.595%   $96.8198   $96.82   $96.80   $96.80  
  Purchase #7 $169.81   3.703%   $176.0981   $176.10   $176.10   $176.10  
  7 purchase totals = $1,032.87       $1,115.2799   $1,115.28   $1,115.30   $1,115.20