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 $44.37   10.313%   $48.9459   $48.95   $48.95   $48.90  
  Purchase #2 $155.28   8.300%   $168.1682   $168.17   $168.15   $168.20  
  Purchase #3 $125.48   6.701%   $133.8884   $133.89   $133.90   $133.90  
  Purchase #4 $240.93   11.509%   $268.6586   $268.66   $268.65   $268.70  
  Purchase #5 $233.72   13.177%   $264.5173   $264.52   $264.50   $264.50  
  Purchase #6 $185.55   9.460%   $203.103   $203.10   $203.10   $203.10  
  Purchase #7 $140.52   8.593%   $152.5949   $152.59   $152.60   $152.60  
  7 purchase totals = $1,125.85       $1,239.8763   $1,239.88   $1,239.85   $1,239.90