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 $249.46   4.623%   $260.9925   $260.99   $261.00   $261.00  
  Purchase #2 $90.69   12.849%   $102.3428   $102.34   $102.35   $102.30  
  Purchase #3 $74.94   3.596%   $77.6348   $77.63   $77.65   $77.60  
  Purchase #4 $246.62   11.761%   $275.625   $275.63   $275.65   $275.60  
  Purchase #5 $232.59   8.142%   $251.5275   $251.53   $251.55   $251.50  
  Purchase #6 $122.73   12.823%   $138.4677   $138.47   $138.45   $138.50  
  Purchase #7 $5.93   8.539%   $6.4364   $6.44   $6.45   $6.40  
  7 purchase totals = $1,022.96       $1,113.0267   $1,113.03   $1,113.10   $1,112.90