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 $162.73   3.136%   $167.8332   $167.83   $167.85   $167.80  
  Purchase #2 $58.51   5.471%   $61.7111   $61.71   $61.70   $61.70  
  Purchase #3 $154.87   6.227%   $164.5138   $164.51   $164.50   $164.50  
  Purchase #4 $184.36   6.165%   $195.7258   $195.73   $195.75   $195.70  
  Purchase #5 $212.47   10.391%   $234.5478   $234.55   $234.55   $234.50  
  Purchase #6 $80.75   8.418%   $87.5475   $87.55   $87.55   $87.50  
  Purchase #7 $53.90   6.434%   $57.3679   $57.37   $57.35   $57.40  
  7 purchase totals = $907.59       $969.2471   $969.25   $969.25   $969.10