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 $68.28   9.867%   $75.0172   $75.02   $75.00   $75.00  
  Purchase #2 $244.88   8.738%   $266.2776   $266.28   $266.30   $266.30  
  Purchase #3 $142.86   8.574%   $155.1088   $155.11   $155.10   $155.10  
  Purchase #4 $210.90   5.821%   $223.1765   $223.18   $223.20   $223.20  
  Purchase #5 $98.76   8.133%   $106.7922   $106.79   $106.80   $106.80  
  Purchase #6 $125.26   9.795%   $137.5292   $137.53   $137.55   $137.50  
  Purchase #7 $46.30   3.335%   $47.8441   $47.84   $47.85   $47.80  
  7 purchase totals = $937.24       $1,011.7456   $1,011.75   $1,011.80   $1,011.70