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 $86.95   11.372%   $96.838   $96.84   $96.85   $96.80  
  Purchase #2 $60.47   13.356%   $68.5464   $68.55   $68.55   $68.50  
  Purchase #3 $237.71   4.461%   $248.3142   $248.31   $248.30   $248.30  
  Purchase #4 $108.53   13.369%   $123.0394   $123.04   $123.05   $123.00  
  Purchase #5 $132.99   3.805%   $138.0503   $138.05   $138.05   $138.10  
  Purchase #6 $18.67   10.820%   $20.6901   $20.69   $20.70   $20.70  
  Purchase #7 $95.74   13.753%   $108.9071   $108.91   $108.90   $108.90  
  7 purchase totals = $741.06       $804.3855   $804.39   $804.40   $804.30