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 $172.50   12.716%   $194.4351   $194.44   $194.45   $194.40  
  Purchase #2 $173.28   4.662%   $181.3583   $181.36   $181.35   $181.40  
  Purchase #3 $24.93   4.241%   $25.9873   $25.99   $26.00   $26.00  
  Purchase #4 $52.62   11.516%   $58.6797   $58.68   $58.70   $58.70  
  Purchase #5 $176.67   6.781%   $188.65   $188.65   $188.65   $188.70  
  Purchase #6 $177.32   10.670%   $196.24   $196.24   $196.25   $196.20  
  Purchase #7 $140.50   5.347%   $148.0125   $148.01   $148.00   $148.00  
  7 purchase totals = $917.82       $993.3629   $993.37   $993.40   $993.40