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 $88.57   8.261%   $95.8868   $95.89   $95.90   $95.90  
  Purchase #2 $210.59   4.444%   $219.9486   $219.95   $219.95   $219.90  
  Purchase #3 $166.56   8.424%   $180.591   $180.59   $180.60   $180.60  
  Purchase #4 $115.29   7.796%   $124.278   $124.28   $124.30   $124.30  
  Purchase #5 $250.29   11.680%   $279.5239   $279.52   $279.50   $279.50  
  Purchase #6 $25.86   12.155%   $29.0033   $29.00   $29.00   $29.00  
  Purchase #7 $248.73   5.725%   $262.9698   $262.97   $262.95   $263.00  
  7 purchase totals = $1,105.89       $1,192.2014   $1,192.20   $1,192.20   $1,192.20