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 $206.33   6.636%   $220.0221   $220.02   $220.00   $220.00  
  Purchase #2 $219.86   9.540%   $240.8346   $240.83   $240.85   $240.80  
  Purchase #3 $50.77   9.707%   $55.6982   $55.70   $55.70   $55.70  
  Purchase #4 $246.33   3.321%   $254.5106   $254.51   $254.50   $254.50  
  Purchase #5 $187.44   9.318%   $204.9057   $204.91   $204.90   $204.90  
  Purchase #6 $249.53   3.408%   $258.034   $258.03   $258.05   $258.00  
  Purchase #7 $67.82   9.267%   $74.1049   $74.10   $74.10   $74.10  
  7 purchase totals = $1,228.08       $1,308.1101   $1,308.10   $1,308.10   $1,308.00