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 $189.36   8.241%   $204.9652   $204.97   $204.95   $205.00  
  Purchase #2 $86.28   7.123%   $92.4257   $92.43   $92.45   $92.40  
  Purchase #3 $215.76   5.486%   $227.5966   $227.60   $227.60   $227.60  
  Purchase #4 $5.54   8.423%   $6.0066   $6.01   $6.00   $6.00  
  Purchase #5 $87.76   5.289%   $92.4016   $92.40   $92.40   $92.40  
  Purchase #6 $181.26   8.446%   $196.5692   $196.57   $196.55   $196.60  
  Purchase #7 $93.50   6.862%   $99.916   $99.92   $99.90   $99.90  
  7 purchase totals = $859.46       $919.8809   $919.90   $919.85   $919.90