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 $233.36   11.415%   $259.998   $260.00   $260.00   $260.00  
  Purchase #2 $15.49   13.177%   $17.5311   $17.53   $17.55   $17.50  
  Purchase #3 $124.67   12.820%   $140.6527   $140.65   $140.65   $140.70  
  Purchase #4 $175.78   11.699%   $196.3445   $196.34   $196.35   $196.30  
  Purchase #5 $143.51   8.781%   $156.1116   $156.11   $156.10   $156.10  
  Purchase #6 $133.77   10.573%   $147.9135   $147.91   $147.90   $147.90  
  Purchase #7 $204.37   11.255%   $227.3718   $227.37   $227.35   $227.40  
  7 purchase totals = $1,030.95       $1,145.9232   $1,145.91   $1,145.90   $1,145.90