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 $83.61   11.756%   $93.4392   $93.44   $93.45   $93.40  
  Purchase #2 $171.42   3.755%   $177.8568   $177.86   $177.85   $177.90  
  Purchase #3 $176.42   8.653%   $191.6856   $191.69   $191.70   $191.70  
  Purchase #4 $117.49   7.850%   $126.713   $126.71   $126.70   $126.70  
  Purchase #5 $93.54   9.645%   $102.5619   $102.56   $102.55   $102.60  
  Purchase #6 $73.62   4.504%   $76.9358   $76.94   $76.95   $76.90  
  Purchase #7 $211.31   11.162%   $234.8964   $234.90   $234.90   $234.90  
  7 purchase totals = $927.41       $1,004.0887   $1,004.10   $1,004.10   $1,004.10