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 $153.67   5.772%   $162.5398   $162.54   $162.55   $162.50  
  Purchase #2 $221.26   9.582%   $242.4611   $242.46   $242.45   $242.50  
  Purchase #3 $245.54   9.248%   $268.2475   $268.25   $268.25   $268.20  
  Purchase #4 $29.67   12.333%   $33.3292   $33.33   $33.35   $33.30  
  Purchase #5 $115.79   8.537%   $125.675   $125.68   $125.70   $125.70  
  Purchase #6 $162.66   10.576%   $179.8629   $179.86   $179.85   $179.90  
  Purchase #7 $174.80   5.843%   $185.0136   $185.01   $185.00   $185.00  
  7 purchase totals = $1,103.39       $1,197.1291   $1,197.13   $1,197.15   $1,197.10