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 $89.44   8.493%   $97.0361   $97.04   $97.05   $97.00  
  Purchase #2 $246.56   4.579%   $257.85   $257.85   $257.85   $257.90  
  Purchase #3 $32.34   4.166%   $33.6873   $33.69   $33.70   $33.70  
  Purchase #4 $235.88   9.830%   $259.067   $259.07   $259.05   $259.10  
  Purchase #5 $135.59   10.725%   $150.132   $150.13   $150.15   $150.10  
  Purchase #6 $213.53   12.409%   $240.0269   $240.03   $240.05   $240.00  
  Purchase #7 $143.64   12.575%   $161.7027   $161.70   $161.70   $161.70  
  7 purchase totals = $1,096.98       $1,199.5020   $1,199.51   $1,199.55   $1,199.50