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 $55.64   10.147%   $61.2858   $61.29   $61.30   $61.30  
  Purchase #2 $73.65   4.800%   $77.1852   $77.19   $77.20   $77.20  
  Purchase #3 $36.46   11.577%   $40.681   $40.68   $40.70   $40.70  
  Purchase #4 $141.41   5.705%   $149.4774   $149.48   $149.50   $149.50  
  Purchase #5 $155.80   7.670%   $167.7499   $167.75   $167.75   $167.70  
  Purchase #6 $175.88   5.763%   $186.016   $186.02   $186.00   $186.00  
  Purchase #7 $82.32   11.142%   $91.4921   $91.49   $91.50   $91.50  
  7 purchase totals = $721.16       $773.8874   $773.90   $773.95   $773.90