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 $60.26   13.864%   $68.6144   $68.61   $68.60   $68.60  
  Purchase #2 $156.32   3.266%   $161.4254   $161.43   $161.45   $161.40  
  Purchase #3 $201.31   9.715%   $220.8673   $220.87   $220.85   $220.90  
  Purchase #4 $213.61   11.816%   $238.8502   $238.85   $238.85   $238.90  
  Purchase #5 $106.27   5.588%   $112.2084   $112.21   $112.20   $112.20  
  Purchase #6 $17.54   8.674%   $19.0614   $19.06   $19.05   $19.10  
  Purchase #7 $242.63   8.301%   $262.7707   $262.77   $262.75   $262.80  
  7 purchase totals = $997.94       $1,083.7978   $1,083.80   $1,083.75   $1,083.90