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 $69.52   9.818%   $76.3455   $76.35   $76.35   $76.30  
  Purchase #2 $228.59   8.287%   $247.5333   $247.53   $247.55   $247.50  
  Purchase #3 $132.38   4.202%   $137.9426   $137.94   $137.95   $137.90  
  Purchase #4 $114.33   8.174%   $123.6753   $123.68   $123.70   $123.70  
  Purchase #5 $70.77   12.183%   $79.3919   $79.39   $79.40   $79.40  
  Purchase #6 $250.92   11.415%   $279.5625   $279.56   $279.55   $279.60  
  Purchase #7 $163.35   12.285%   $183.4175   $183.42   $183.40   $183.40  
  7 purchase totals = $1,029.86       $1,127.8686   $1,127.87   $1,127.90   $1,127.80