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 $91.37   10.561%   $101.0196   $101.02   $101.00   $101.00  
  Purchase #2 $55.55   5.121%   $58.3947   $58.39   $58.40   $58.40  
  Purchase #3 $171.92   13.357%   $194.8834   $194.88   $194.90   $194.90  
  Purchase #4 $185.59   8.872%   $202.0555   $202.06   $202.05   $202.10  
  Purchase #5 $54.99   5.530%   $58.0309   $58.03   $58.05   $58.00  
  Purchase #6 $200.68   6.863%   $214.4527   $214.45   $214.45   $214.50  
  Purchase #7 $143.97   8.822%   $156.671   $156.67   $156.65   $156.70  
  7 purchase totals = $904.07       $985.5078   $985.50   $985.50   $985.60