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 $216.41   12.735%   $243.9698   $243.97   $243.95   $244.00  
  Purchase #2 $71.76   11.331%   $79.8911   $79.89   $79.90   $79.90  
  Purchase #3 $107.34   8.591%   $116.5616   $116.56   $116.55   $116.60  
  Purchase #4 $139.87   10.106%   $154.0053   $154.01   $154.00   $154.00  
  Purchase #5 $190.43   12.836%   $214.8736   $214.87   $214.85   $214.90  
  Purchase #6 $190.52   12.535%   $214.4017   $214.40   $214.40   $214.40  
  Purchase #7 $38.27   7.666%   $41.2038   $41.20   $41.20   $41.20  
  7 purchase totals = $954.60       $1,064.9069   $1,064.90   $1,064.85   $1,065.00