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 $60.95   9.444%   $66.7061   $66.71   $66.70   $66.70  
  Purchase #2 $191.65   13.544%   $217.6071   $217.61   $217.60   $217.60  
  Purchase #3 $70.45   5.867%   $74.5833   $74.58   $74.60   $74.60  
  Purchase #4 $127.39   8.810%   $138.6131   $138.61   $138.60   $138.60  
  Purchase #5 $218.32   9.840%   $239.8027   $239.80   $239.80   $239.80  
  Purchase #6 $50.93   12.315%   $57.202   $57.20   $57.20   $57.20  
  Purchase #7 $41.61   7.675%   $44.8036   $44.80   $44.80   $44.80  
  7 purchase totals = $761.30       $839.3179   $839.31   $839.30   $839.30