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 $246.36   12.282%   $276.6179   $276.62   $276.60   $276.60  
  Purchase #2 $146.63   6.257%   $155.8046   $155.80   $155.80   $155.80  
  Purchase #3 $17.47   6.317%   $18.5736   $18.57   $18.55   $18.60  
  Purchase #4 $30.88   9.231%   $33.7305   $33.73   $33.75   $33.70  
  Purchase #5 $190.94   11.581%   $213.0528   $213.05   $213.05   $213.10  
  Purchase #6 $190.72   4.213%   $198.755   $198.76   $198.75   $198.80  
  Purchase #7 $131.25   12.509%   $147.6681   $147.67   $147.65   $147.70  
  7 purchase totals = $954.25       $1,044.2025   $1,044.20   $1,044.15   $1,044.30