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 $246.74   11.277%   $274.5649   $274.56   $274.55   $274.60  
  Purchase #2 $34.37   9.774%   $37.7293   $37.73   $37.75   $37.70  
  Purchase #3 $232.74   10.314%   $256.7448   $256.74   $256.75   $256.70  
  Purchase #4 $33.94   12.748%   $38.2667   $38.27   $38.25   $38.30  
  Purchase #5 $21.95   10.253%   $24.2005   $24.20   $24.20   $24.20  
  Purchase #6 $156.54   12.346%   $175.8664   $175.87   $175.85   $175.90  
  Purchase #7 $226.83   12.373%   $254.8957   $254.90   $254.90   $254.90  
  7 purchase totals = $953.11       $1,062.2683   $1,062.27   $1,062.25   $1,062.30