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 $250.74   5.213%   $263.8111   $263.81   $263.80   $263.80  
  Purchase #2 $57.97   11.257%   $64.4957   $64.50   $64.50   $64.50  
  Purchase #3 $29.32   5.773%   $31.0126   $31.01   $31.00   $31.00  
  Purchase #4 $197.30   5.395%   $207.9443   $207.94   $207.95   $207.90  
  Purchase #5 $63.96   3.728%   $66.3444   $66.34   $66.35   $66.30  
  Purchase #6 $162.55   9.655%   $178.2442   $178.24   $178.25   $178.20  
  Purchase #7 $23.35   4.722%   $24.4526   $24.45   $24.45   $24.50  
  7 purchase totals = $785.19       $836.3049   $836.29   $836.30   $836.20