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 $17.39   12.670%   $19.5933   $19.59   $19.60   $19.60  
  Purchase #2 $95.52   8.464%   $103.6048   $103.60   $103.60   $103.60  
  Purchase #3 $204.44   10.206%   $225.3051   $225.31   $225.30   $225.30  
  Purchase #4 $233.28   12.873%   $263.3101   $263.31   $263.30   $263.30  
  Purchase #5 $224.66   7.137%   $240.694   $240.69   $240.70   $240.70  
  Purchase #6 $134.83   12.838%   $152.1395   $152.14   $152.15   $152.10  
  Purchase #7 $23.87   7.856%   $25.7452   $25.75   $25.75   $25.70  
  7 purchase totals = $933.99       $1,030.3920   $1,030.39   $1,030.40   $1,030.30