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 $93.43   8.372%   $101.252   $101.25   $101.25   $101.30  
  Purchase #2 $45.40   11.381%   $50.567   $50.57   $50.55   $50.60  
  Purchase #3 $28.58   5.241%   $30.0779   $30.08   $30.10   $30.10  
  Purchase #4 $181.94   4.622%   $190.3493   $190.35   $190.35   $190.30  
  Purchase #5 $52.29   10.793%   $57.9337   $57.93   $57.95   $57.90  
  Purchase #6 $34.92   9.386%   $38.1976   $38.20   $38.20   $38.20  
  Purchase #7 $131.42   8.695%   $142.847   $142.85   $142.85   $142.80  
  7 purchase totals = $567.98       $611.2245   $611.23   $611.25   $611.20