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 $73.35   13.427%   $83.1987   $83.20   $83.20   $83.20  
  Purchase #2 $125.32   9.329%   $137.0111   $137.01   $137.00   $137.00  
  Purchase #3 $53.77   13.626%   $61.0967   $61.10   $61.10   $61.10  
  Purchase #4 $152.72   7.411%   $164.0381   $164.04   $164.05   $164.00  
  Purchase #5 $71.95   3.405%   $74.3999   $74.40   $74.40   $74.40  
  Purchase #6 $94.59   13.157%   $107.0352   $107.04   $107.05   $107.00  
  Purchase #7 $118.41   5.543%   $124.9735   $124.97   $124.95   $125.00  
  7 purchase totals = $690.11       $751.7532   $751.76   $751.75   $751.70