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 $57.58   5.870%   $60.9599   $60.96   $60.95   $61.00  
  Purchase #2 $94.93   10.611%   $105.003   $105.00   $105.00   $105.00  
  Purchase #3 $14.78   13.493%   $16.7743   $16.77   $16.75   $16.80  
  Purchase #4 $148.55   6.439%   $158.1151   $158.12   $158.10   $158.10  
  Purchase #5 $165.26   9.548%   $181.039   $181.04   $181.05   $181.00  
  Purchase #6 $9.57   5.855%   $10.1303   $10.13   $10.15   $10.10  
  Purchase #7 $180.82   5.382%   $190.5517   $190.55   $190.55   $190.60  
  7 purchase totals = $671.49       $722.5733   $722.57   $722.55   $722.60