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 $71.54   8.503%   $77.623   $77.62   $77.60   $77.60  
  Purchase #2 $28.51   8.276%   $30.8695   $30.87   $30.85   $30.90  
  Purchase #3 $175.84   11.192%   $195.52   $195.52   $195.50   $195.50  
  Purchase #4 $217.55   9.469%   $238.1498   $238.15   $238.15   $238.10  
  Purchase #5 $9.27   9.119%   $10.1153   $10.12   $10.10   $10.10  
  Purchase #6 $107.52   10.159%   $118.443   $118.44   $118.45   $118.40  
  Purchase #7 $47.36   11.729%   $52.9149   $52.91   $52.90   $52.90  
  7 purchase totals = $657.59       $723.6355   $723.63   $723.55   $723.50