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 $95.58   8.321%   $103.5332   $103.53   $103.55   $103.50  
  Purchase #2 $134.35   10.862%   $148.9431   $148.94   $148.95   $148.90  
  Purchase #3 $24.28   4.258%   $25.3138   $25.31   $25.30   $25.30  
  Purchase #4 $56.35   8.334%   $61.0462   $61.05   $61.05   $61.00  
  Purchase #5 $116.92   4.531%   $122.2176   $122.22   $122.20   $122.20  
  Purchase #6 $124.86   3.747%   $129.5385   $129.54   $129.55   $129.50  
  Purchase #7 $164.56   6.211%   $174.7808   $174.78   $174.80   $174.80  
  7 purchase totals = $716.90       $765.3732   $765.37   $765.40   $765.20