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 $67.84   3.250%   $70.0448   $70.04   $70.05   $70.00  
  Purchase #2 $227.94   13.451%   $258.6002   $258.60   $258.60   $258.60  
  Purchase #3 $72.70   10.370%   $80.239   $80.24   $80.25   $80.20  
  Purchase #4 $172.32   7.215%   $184.7529   $184.75   $184.75   $184.80  
  Purchase #5 $158.95   10.122%   $175.0389   $175.04   $175.05   $175.00  
  Purchase #6 $51.99   13.268%   $58.888   $58.89   $58.90   $58.90  
  Purchase #7 $196.45   4.478%   $205.247   $205.25   $205.25   $205.20  
  7 purchase totals = $948.19       $1,032.8108   $1,032.81   $1,032.85   $1,032.70