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 $26.65   6.759%   $28.4513   $28.45   $28.45   $28.50  
  Purchase #2 $136.64   5.117%   $143.6319   $143.63   $143.65   $143.60  
  Purchase #3 $135.65   10.271%   $149.5826   $149.58   $149.60   $149.60  
  Purchase #4 $208.58   5.578%   $220.2146   $220.21   $220.20   $220.20  
  Purchase #5 $209.89   6.789%   $224.1394   $224.14   $224.15   $224.10  
  Purchase #6 $102.83   3.283%   $106.2059   $106.21   $106.20   $106.20  
  Purchase #7 $126.75   13.574%   $143.955   $143.96   $143.95   $144.00  
  7 purchase totals = $946.99       $1,016.1807   $1,016.18   $1,016.20   $1,016.20