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 $241.96   13.215%   $273.935   $273.94   $273.95   $273.90  
  Purchase #2 $111.47   8.420%   $120.8558   $120.86   $120.85   $120.90  
  Purchase #3 $161.46   10.613%   $178.5957   $178.60   $178.60   $178.60  
  Purchase #4 $219.71   12.449%   $247.0617   $247.06   $247.05   $247.10  
  Purchase #5 $22.67   8.295%   $24.5505   $24.55   $24.55   $24.60  
  Purchase #6 $178.98   12.332%   $201.0518   $201.05   $201.05   $201.10  
  Purchase #7 $18.91   13.564%   $21.475   $21.48   $21.50   $21.50  
  7 purchase totals = $955.16       $1,067.5255   $1,067.54   $1,067.55   $1,067.70