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 $84.94   5.206%   $89.362   $89.36   $89.35   $89.40  
  Purchase #2 $85.53   3.531%   $88.5501   $88.55   $88.55   $88.60  
  Purchase #3 $229.38   13.422%   $260.1674   $260.17   $260.15   $260.20  
  Purchase #4 $192.49   4.287%   $200.742   $200.74   $200.75   $200.70  
  Purchase #5 $187.29   5.741%   $198.0423   $198.04   $198.05   $198.00  
  Purchase #6 $179.55   8.411%   $194.652   $194.65   $194.65   $194.70  
  Purchase #7 $186.91   9.800%   $205.2272   $205.23   $205.25   $205.20  
  7 purchase totals = $1,146.09       $1,236.7430   $1,236.74   $1,236.75   $1,236.80