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 $59.87   13.861%   $68.1686   $68.17   $68.15   $68.20  
  Purchase #2 $68.37   10.323%   $75.4278   $75.43   $75.45   $75.40  
  Purchase #3 $174.88   13.576%   $198.6217   $198.62   $198.60   $198.60  
  Purchase #4 $138.73   9.511%   $151.9246   $151.92   $151.90   $151.90  
  Purchase #5 $195.72   10.787%   $216.8323   $216.83   $216.85   $216.80  
  Purchase #6 $198.48   10.418%   $219.1576   $219.16   $219.15   $219.20  
  Purchase #7 $76.80   3.733%   $79.6669   $79.67   $79.65   $79.70  
  7 purchase totals = $912.85       $1,009.7995   $1,009.80   $1,009.75   $1,009.80