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 $164.43   13.432%   $186.5162   $186.52   $186.50   $186.50  
  Purchase #2 $62.77   7.786%   $67.6573   $67.66   $67.65   $67.70  
  Purchase #3 $152.41   9.525%   $166.9271   $166.93   $166.95   $166.90  
  Purchase #4 $240.86   11.140%   $267.6918   $267.69   $267.70   $267.70  
  Purchase #5 $14.69   9.696%   $16.1143   $16.11   $16.10   $16.10  
  Purchase #6 $189.99   9.192%   $207.4539   $207.45   $207.45   $207.50  
  Purchase #7 $126.49   10.848%   $140.2116   $140.21   $140.20   $140.20  
  7 purchase totals = $951.64       $1,052.5722   $1,052.57   $1,052.55   $1,052.60