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 $76.30   9.255%   $83.3616   $83.36   $83.35   $83.40  
  Purchase #2 $192.97   9.154%   $210.6345   $210.63   $210.65   $210.60  
  Purchase #3 $14.96   4.270%   $15.5988   $15.60   $15.60   $15.60  
  Purchase #4 $53.35   13.694%   $60.6557   $60.66   $60.65   $60.70  
  Purchase #5 $100.87   6.105%   $107.0281   $107.03   $107.05   $107.00  
  Purchase #6 $73.70   8.759%   $80.1554   $80.16   $80.15   $80.20  
  Purchase #7 $89.93   6.511%   $95.7853   $95.79   $95.80   $95.80  
  7 purchase totals = $602.08       $653.2194   $653.23   $653.25   $653.30