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 $106.92   11.874%   $119.6157   $119.62   $119.60   $119.60  
  Purchase #2 $134.74   3.133%   $138.9614   $138.96   $138.95   $139.00  
  Purchase #3 $194.62   13.663%   $221.2109   $221.21   $221.20   $221.20  
  Purchase #4 $211.61   11.250%   $235.4161   $235.42   $235.40   $235.40  
  Purchase #5 $177.72   13.801%   $202.2471   $202.25   $202.25   $202.20  
  Purchase #6 $74.57   11.269%   $82.9733   $82.97   $82.95   $83.00  
  Purchase #7 $82.75   4.393%   $86.3852   $86.39   $86.40   $86.40  
  7 purchase totals = $982.93       $1,086.8097   $1,086.82   $1,086.75   $1,086.80