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 $56.39   8.629%   $61.2559   $61.26   $61.25   $61.30  
  Purchase #2 $34.36   13.394%   $38.9622   $38.96   $38.95   $39.00  
  Purchase #3 $58.49   10.393%   $64.5689   $64.57   $64.55   $64.60  
  Purchase #4 $32.79   5.637%   $34.6384   $34.64   $34.65   $34.60  
  Purchase #5 $226.98   5.321%   $239.0576   $239.06   $239.05   $239.10  
  Purchase #6 $211.91   9.260%   $231.5329   $231.53   $231.55   $231.50  
  Purchase #7 $60.43   7.863%   $65.1816   $65.18   $65.20   $65.20  
  7 purchase totals = $681.35       $735.1975   $735.20   $735.20   $735.30