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 $75.91   12.364%   $85.2955   $85.30   $85.30   $85.30  
  Purchase #2 $143.74   9.209%   $156.977   $156.98   $157.00   $157.00  
  Purchase #3 $65.54   5.735%   $69.2987   $69.30   $69.30   $69.30  
  Purchase #4 $218.64   13.827%   $248.8714   $248.87   $248.85   $248.90  
  Purchase #5 $223.59   3.353%   $231.087   $231.09   $231.10   $231.10  
  Purchase #6 $173.84   6.825%   $185.7046   $185.70   $185.70   $185.70  
  Purchase #7 $182.56   8.130%   $197.4021   $197.40   $197.40   $197.40  
  7 purchase totals = $1,083.82       $1,174.6363   $1,174.64   $1,174.65   $1,174.70