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 $17.94   5.159%   $18.8655   $18.87   $18.85   $18.90  
  Purchase #2 $68.43   8.526%   $74.2643   $74.26   $74.25   $74.30  
  Purchase #3 $89.85   11.298%   $100.0013   $100.00   $100.00   $100.00  
  Purchase #4 $210.38   8.872%   $229.0449   $229.04   $229.05   $229.00  
  Purchase #5 $95.53   4.769%   $100.0858   $100.09   $100.10   $100.10  
  Purchase #6 $17.70   7.690%   $19.0611   $19.06   $19.05   $19.10  
  Purchase #7 $145.59   10.709%   $161.1812   $161.18   $161.20   $161.20  
  7 purchase totals = $645.42       $702.5041   $702.50   $702.50   $702.60