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 $62.63   12.134%   $70.2295   $70.23   $70.25   $70.20  
  Purchase #2 $245.26   8.719%   $266.6442   $266.64   $266.65   $266.60  
  Purchase #3 $209.63   7.309%   $224.9519   $224.95   $224.95   $225.00  
  Purchase #4 $135.83   6.470%   $144.6182   $144.62   $144.60   $144.60  
  Purchase #5 $218.81   6.559%   $233.1617   $233.16   $233.15   $233.20  
  Purchase #6 $35.44   12.763%   $39.9632   $39.96   $39.95   $40.00  
  Purchase #7 $200.75   11.669%   $224.1755   $224.18   $224.20   $224.20  
  7 purchase totals = $1,108.35       $1,203.7442   $1,203.74   $1,203.75   $1,203.80