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 $134.66   12.618%   $151.6514   $151.65   $151.65   $151.70  
  Purchase #2 $24.52   4.802%   $25.6975   $25.70   $25.70   $25.70  
  Purchase #3 $140.34   4.607%   $146.8055   $146.81   $146.80   $146.80  
  Purchase #4 $212.84   6.328%   $226.3085   $226.31   $226.30   $226.30  
  Purchase #5 $182.38   11.244%   $202.8868   $202.89   $202.90   $202.90  
  Purchase #6 $239.63   6.504%   $255.2155   $255.22   $255.20   $255.20  
  Purchase #7 $178.34   8.180%   $192.9282   $192.93   $192.95   $192.90  
  7 purchase totals = $1,112.71       $1,201.4934   $1,201.51   $1,201.50   $1,201.50