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 $151.94   5.839%   $160.8118   $160.81   $160.80   $160.80  
  Purchase #2 $69.59   11.382%   $77.5107   $77.51   $77.50   $77.50  
  Purchase #3 $182.34   10.482%   $201.4529   $201.45   $201.45   $201.50  
  Purchase #4 $56.85   8.262%   $61.5469   $61.55   $61.55   $61.50  
  Purchase #5 $225.84   13.380%   $256.0574   $256.06   $256.05   $256.10  
  Purchase #6 $155.36   12.411%   $174.6417   $174.64   $174.65   $174.60  
  Purchase #7 $22.96   13.315%   $26.0171   $26.02   $26.00   $26.00  
  7 purchase totals = $864.88       $958.0385   $958.04   $958.00   $958.00