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 $192.69   7.562%   $207.2612   $207.26   $207.25   $207.30  
  Purchase #2 $226.99   6.331%   $241.3607   $241.36   $241.35   $241.40  
  Purchase #3 $105.27   11.677%   $117.5624   $117.56   $117.55   $117.60  
  Purchase #4 $247.81   4.116%   $258.0099   $258.01   $258.00   $258.00  
  Purchase #5 $229.55   7.323%   $246.3599   $246.36   $246.35   $246.40  
  Purchase #6 $231.87   11.428%   $258.3681   $258.37   $258.35   $258.40  
  Purchase #7 $26.43   12.317%   $29.6854   $29.69   $29.70   $29.70  
  7 purchase totals = $1,260.61       $1,358.6076   $1,358.61   $1,358.55   $1,358.80