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 $86.49   8.737%   $94.0466   $94.05   $94.05   $94.00  
  Purchase #2 $223.86   13.318%   $253.6737   $253.67   $253.65   $253.70  
  Purchase #3 $23.25   12.780%   $26.2214   $26.22   $26.20   $26.20  
  Purchase #4 $172.51   10.261%   $190.2113   $190.21   $190.20   $190.20  
  Purchase #5 $104.35   3.805%   $108.3205   $108.32   $108.30   $108.30  
  Purchase #6 $16.30   13.803%   $18.5499   $18.55   $18.55   $18.50  
  Purchase #7 $200.97   4.353%   $209.7182   $209.72   $209.70   $209.70  
  7 purchase totals = $827.73       $900.7416   $900.74   $900.65   $900.60