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 $232.37   9.115%   $253.5505   $253.55   $253.55   $253.60  
  Purchase #2 $72.91   5.623%   $77.0097   $77.01   $77.00   $77.00  
  Purchase #3 $82.44   6.255%   $87.5966   $87.60   $87.60   $87.60  
  Purchase #4 $124.63   5.140%   $131.036   $131.04   $131.05   $131.00  
  Purchase #5 $105.52   11.388%   $117.5366   $117.54   $117.55   $117.50  
  Purchase #6 $211.82   10.670%   $234.4212   $234.42   $234.40   $234.40  
  Purchase #7 $60.93   8.122%   $65.8787   $65.88   $65.90   $65.90  
  7 purchase totals = $890.62       $967.0293   $967.04   $967.05   $967.00