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 $186.37   7.846%   $200.9926   $200.99   $201.00   $201.00  
  Purchase #2 $46.95   3.384%   $48.5388   $48.54   $48.55   $48.50  
  Purchase #3 $92.89   4.512%   $97.0812   $97.08   $97.10   $97.10  
  Purchase #4 $95.72   8.153%   $103.5241   $103.52   $103.50   $103.50  
  Purchase #5 $152.62   10.255%   $168.2712   $168.27   $168.25   $168.30  
  Purchase #6 $193.60   7.817%   $208.7337   $208.73   $208.75   $208.70  
  Purchase #7 $201.69   3.377%   $208.5011   $208.50   $208.50   $208.50  
  7 purchase totals = $969.84       $1,035.6427   $1,035.63   $1,035.65   $1,035.60