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 $177.54   12.397%   $199.5496   $199.55   $199.55   $199.50  
  Purchase #2 $104.97   11.778%   $117.3334   $117.33   $117.35   $117.30  
  Purchase #3 $144.61   6.442%   $153.9258   $153.93   $153.95   $153.90  
  Purchase #4 $58.41   8.139%   $63.164   $63.16   $63.15   $63.20  
  Purchase #5 $98.58   6.477%   $104.965   $104.97   $104.95   $105.00  
  Purchase #6 $21.55   11.361%   $23.9983   $24.00   $24.00   $24.00  
  Purchase #7 $161.84   7.799%   $174.4619   $174.46   $174.45   $174.50  
  7 purchase totals = $767.50       $837.3980   $837.40   $837.40   $837.40