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 $185.79   13.849%   $211.5201   $211.52   $211.50   $211.50  
  Purchase #2 $141.41   10.285%   $155.954   $155.95   $155.95   $156.00  
  Purchase #3 $200.55   12.532%   $225.6829   $225.68   $225.70   $225.70  
  Purchase #4 $57.64   8.453%   $62.5123   $62.51   $62.50   $62.50  
  Purchase #5 $49.79   3.228%   $51.3972   $51.40   $51.40   $51.40  
  Purchase #6 $247.66   11.861%   $277.035   $277.04   $277.05   $277.00  
  Purchase #7 $9.79   12.798%   $11.0429   $11.04   $11.05   $11.00  
  7 purchase totals = $892.63       $995.1444   $995.14   $995.15   $995.10