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 $178.79   9.791%   $196.2953   $196.30   $196.30   $196.30  
  Purchase #2 $230.66   6.216%   $244.9978   $245.00   $245.00   $245.00  
  Purchase #3 $185.49   10.323%   $204.6381   $204.64   $204.65   $204.60  
  Purchase #4 $13.69   13.294%   $15.5099   $15.51   $15.50   $15.50  
  Purchase #5 $133.94   6.783%   $143.0252   $143.03   $143.05   $143.00  
  Purchase #6 $169.78   3.670%   $176.0109   $176.01   $176.00   $176.00  
  Purchase #7 $78.90   12.617%   $88.8548   $88.85   $88.85   $88.90  
  7 purchase totals = $991.25       $1,069.3320   $1,069.34   $1,069.35   $1,069.30