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 $66.93   11.341%   $74.5205   $74.52   $74.50   $74.50  
  Purchase #2 $188.54   11.239%   $209.73   $209.73   $209.75   $209.70  
  Purchase #3 $79.37   11.620%   $88.5928   $88.59   $88.60   $88.60  
  Purchase #4 $57.46   7.795%   $61.939   $61.94   $61.95   $61.90  
  Purchase #5 $187.25   8.533%   $203.228   $203.23   $203.25   $203.20  
  Purchase #6 $232.67   8.628%   $252.7448   $252.74   $252.75   $252.70  
  Purchase #7 $203.68   5.179%   $214.2286   $214.23   $214.25   $214.20  
  7 purchase totals = $1,015.90       $1,104.9837   $1,104.98   $1,105.05   $1,104.80