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 $66.71   8.143%   $72.1422   $72.14   $72.15   $72.10  
  Purchase #2 $234.75   8.303%   $254.2413   $254.24   $254.25   $254.20  
  Purchase #3 $240.37   4.704%   $251.677   $251.68   $251.70   $251.70  
  Purchase #4 $22.47   4.874%   $23.5652   $23.57   $23.55   $23.60  
  Purchase #5 $24.55   8.312%   $26.5906   $26.59   $26.60   $26.60  
  Purchase #6 $149.53   6.459%   $159.1881   $159.19   $159.20   $159.20  
  Purchase #7 $193.71   10.742%   $214.5183   $214.52   $214.50   $214.50  
  7 purchase totals = $932.09       $1,001.9227   $1,001.93   $1,001.95   $1,001.90