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 $176.98   9.554%   $193.8887   $193.89   $193.90   $193.90  
  Purchase #2 $210.47   11.106%   $233.8448   $233.84   $233.85   $233.80  
  Purchase #3 $70.90   9.554%   $77.6738   $77.67   $77.65   $77.70  
  Purchase #4 $245.43   8.571%   $266.4658   $266.47   $266.45   $266.50  
  Purchase #5 $27.77   5.272%   $29.234   $29.23   $29.25   $29.20  
  Purchase #6 $154.44   9.629%   $169.311   $169.31   $169.30   $169.30  
  Purchase #7 $229.77   8.513%   $249.3303   $249.33   $249.35   $249.30  
  7 purchase totals = $1,115.76       $1,219.7484   $1,219.74   $1,219.75   $1,219.70