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 $198.25   13.837%   $225.6819   $225.68   $225.70   $225.70  
  Purchase #2 $51.34   12.126%   $57.5655   $57.57   $57.55   $57.60  
  Purchase #3 $153.27   10.663%   $169.6132   $169.61   $169.60   $169.60  
  Purchase #4 $8.65   11.213%   $9.6199   $9.62   $9.60   $9.60  
  Purchase #5 $168.61   9.192%   $184.1086   $184.11   $184.10   $184.10  
  Purchase #6 $104.32   6.468%   $111.0674   $111.07   $111.05   $111.10  
  Purchase #7 $242.39   10.287%   $267.3247   $267.32   $267.30   $267.30  
  7 purchase totals = $926.83       $1,024.9812   $1,024.98   $1,024.90   $1,025.00