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 $85.39   12.734%   $96.2636   $96.26   $96.25   $96.30  
  Purchase #2 $98.28   11.408%   $109.4918   $109.49   $109.50   $109.50  
  Purchase #3 $30.66   6.729%   $32.7231   $32.72   $32.70   $32.70  
  Purchase #4 $211.44   9.506%   $231.5395   $231.54   $231.55   $231.50  
  Purchase #5 $220.92   5.575%   $233.2363   $233.24   $233.25   $233.20  
  Purchase #6 $233.30   5.793%   $246.8151   $246.82   $246.80   $246.80  
  Purchase #7 $113.65   8.797%   $123.6478   $123.65   $123.65   $123.60  
  7 purchase totals = $993.64       $1,073.7172   $1,073.72   $1,073.70   $1,073.60