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 $71.61   12.573%   $80.6135   $80.61   $80.60   $80.60  
  Purchase #2 $24.45   5.719%   $25.8483   $25.85   $25.85   $25.80  
  Purchase #3 $249.82   7.238%   $267.902   $267.90   $267.90   $267.90  
  Purchase #4 $64.90   8.872%   $70.6579   $70.66   $70.65   $70.70  
  Purchase #5 $129.26   13.347%   $146.5123   $146.51   $146.50   $146.50  
  Purchase #6 $187.37   5.732%   $198.11   $198.11   $198.10   $198.10  
  Purchase #7 $201.65   3.430%   $208.5666   $208.57   $208.55   $208.60  
  7 purchase totals = $929.06       $998.2106   $998.21   $998.15   $998.20