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 $85.87   12.146%   $96.2998   $96.30   $96.30   $96.30  
  Purchase #2 $148.26   5.445%   $156.3328   $156.33   $156.35   $156.30  
  Purchase #3 $109.34   7.498%   $117.5383   $117.54   $117.55   $117.50  
  Purchase #4 $87.99   12.631%   $99.104   $99.10   $99.10   $99.10  
  Purchase #5 $201.95   13.261%   $228.7306   $228.73   $228.75   $228.70  
  Purchase #6 $191.55   3.191%   $197.6624   $197.66   $197.65   $197.70  
  Purchase #7 $103.46   3.658%   $107.2446   $107.24   $107.25   $107.20  
  7 purchase totals = $928.42       $1,002.9125   $1,002.90   $1,002.95   $1,002.80