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 $188.69   8.633%   $204.9796   $204.98   $205.00   $205.00  
  Purchase #2 $10.48   4.792%   $10.9822   $10.98   $11.00   $11.00  
  Purchase #3 $95.29   10.609%   $105.3993   $105.40   $105.40   $105.40  
  Purchase #4 $82.71   6.240%   $87.8711   $87.87   $87.85   $87.90  
  Purchase #5 $211.25   5.245%   $222.3301   $222.33   $222.35   $222.30  
  Purchase #6 $173.61   12.494%   $195.3008   $195.30   $195.30   $195.30  
  Purchase #7 $6.96   10.376%   $7.6822   $7.68   $7.70   $7.70  
  7 purchase totals = $768.99       $834.5453   $834.54   $834.60   $834.60