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 $48.60   6.205%   $51.6156   $51.62   $51.60   $51.60  
  Purchase #2 $101.36   13.830%   $115.3781   $115.38   $115.40   $115.40  
  Purchase #3 $10.63   6.414%   $11.3118   $11.31   $11.30   $11.30  
  Purchase #4 $211.58   8.604%   $229.7843   $229.78   $229.80   $229.80  
  Purchase #5 $85.94   5.673%   $90.8154   $90.82   $90.80   $90.80  
  Purchase #6 $243.36   12.262%   $273.2008   $273.20   $273.20   $273.20  
  Purchase #7 $165.61   6.534%   $176.431   $176.43   $176.45   $176.40  
  7 purchase totals = $867.08       $948.5370   $948.54   $948.55   $948.50