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 $58.65   12.461%   $65.9584   $65.96   $65.95   $66.00  
  Purchase #2 $216.99   10.168%   $239.0535   $239.05   $239.05   $239.10  
  Purchase #3 $122.30   3.623%   $126.7309   $126.73   $126.75   $126.70  
  Purchase #4 $37.68   5.472%   $39.7418   $39.74   $39.75   $39.70  
  Purchase #5 $107.65   12.252%   $120.8393   $120.84   $120.85   $120.80  
  Purchase #6 $194.86   13.211%   $220.603   $220.60   $220.60   $220.60  
  Purchase #7 $18.30   8.115%   $19.785   $19.79   $19.80   $19.80  
  7 purchase totals = $756.43       $832.7119   $832.71   $832.75   $832.70