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 $114.93   7.512%   $123.5635   $123.56   $123.55   $123.60  
  Purchase #2 $237.95   3.607%   $246.5329   $246.53   $246.55   $246.50  
  Purchase #3 $47.90   13.668%   $54.447   $54.45   $54.45   $54.40  
  Purchase #4 $147.31   8.782%   $160.2468   $160.25   $160.25   $160.20  
  Purchase #5 $167.25   4.449%   $174.691   $174.69   $174.70   $174.70  
  Purchase #6 $215.81   11.118%   $239.8038   $239.80   $239.80   $239.80  
  Purchase #7 $30.90   5.387%   $32.5646   $32.56   $32.55   $32.60  
  7 purchase totals = $962.05       $1,031.8496   $1,031.84   $1,031.85   $1,031.80