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 $7.65   4.493%   $7.9937   $7.99   $8.00   $8.00  
  Purchase #2 $155.58   3.472%   $160.9817   $160.98   $161.00   $161.00  
  Purchase #3 $153.56   6.603%   $163.6996   $163.70   $163.70   $163.70  
  Purchase #4 $166.28   9.508%   $182.0899   $182.09   $182.10   $182.10  
  Purchase #5 $30.51   11.703%   $34.0806   $34.08   $34.10   $34.10  
  Purchase #6 $77.95   9.120%   $85.059   $85.06   $85.05   $85.10  
  Purchase #7 $93.41   6.567%   $99.5442   $99.54   $99.55   $99.50  
  7 purchase totals = $684.94       $733.4487   $733.44   $733.50   $733.50