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 $87.75   10.791%   $97.2191   $97.22   $97.20   $97.20  
  Purchase #2 $74.50   4.170%   $77.6067   $77.61   $77.60   $77.60  
  Purchase #3 $235.70   5.210%   $247.98   $247.98   $248.00   $248.00  
  Purchase #4 $220.36   12.245%   $247.3431   $247.34   $247.35   $247.30  
  Purchase #5 $130.47   13.182%   $147.6686   $147.67   $147.65   $147.70  
  Purchase #6 $214.70   5.402%   $226.2981   $226.30   $226.30   $226.30  
  Purchase #7 $23.61   3.812%   $24.51   $24.51   $24.50   $24.50  
  7 purchase totals = $987.09       $1,068.6256   $1,068.63   $1,068.60   $1,068.60