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 $240.86   13.789%   $274.0722   $274.07   $274.05   $274.10  
  Purchase #2 $100.67   6.593%   $107.3072   $107.31   $107.30   $107.30  
  Purchase #3 $22.38   10.792%   $24.7952   $24.80   $24.80   $24.80  
  Purchase #4 $223.53   6.823%   $238.7815   $238.78   $238.80   $238.80  
  Purchase #5 $232.75   13.700%   $264.6368   $264.64   $264.65   $264.60  
  Purchase #6 $93.36   3.296%   $96.4371   $96.44   $96.45   $96.40  
  Purchase #7 $162.70   13.382%   $184.4725   $184.47   $184.45   $184.50  
  7 purchase totals = $1,076.25       $1,190.5025   $1,190.51   $1,190.50   $1,190.50