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 $130.82   8.141%   $141.4701   $141.47   $141.45   $141.50  
  Purchase #2 $117.51   8.235%   $127.1869   $127.19   $127.20   $127.20  
  Purchase #3 $238.55   4.764%   $249.9145   $249.91   $249.90   $249.90  
  Purchase #4 $56.77   3.807%   $58.9312   $58.93   $58.95   $58.90  
  Purchase #5 $211.55   3.138%   $218.1884   $218.19   $218.20   $218.20  
  Purchase #6 $87.71   6.491%   $93.4033   $93.40   $93.40   $93.40  
  Purchase #7 $117.62   9.550%   $128.8527   $128.85   $128.85   $128.90  
  7 purchase totals = $960.53       $1,017.9471   $1,017.94   $1,017.95   $1,018.00