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 $153.36   7.130%   $164.2946   $164.29   $164.30   $164.30  
  Purchase #2 $61.45   6.689%   $65.5604   $65.56   $65.55   $65.60  
  Purchase #3 $124.55   4.826%   $130.5608   $130.56   $130.55   $130.60  
  Purchase #4 $28.41   4.706%   $29.747   $29.75   $29.75   $29.70  
  Purchase #5 $166.63   9.811%   $182.9781   $182.98   $183.00   $183.00  
  Purchase #6 $133.52   10.807%   $147.9495   $147.95   $147.95   $147.90  
  Purchase #7 $50.83   7.681%   $54.7343   $54.73   $54.75   $54.70  
  7 purchase totals = $718.75       $775.8247   $775.82   $775.85   $775.80