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 $233.34   5.776%   $246.8177   $246.82   $246.80   $246.80  
  Purchase #2 $186.70   13.380%   $211.6805   $211.68   $211.70   $211.70  
  Purchase #3 $69.31   7.442%   $74.4681   $74.47   $74.45   $74.50  
  Purchase #4 $96.53   13.182%   $109.2546   $109.25   $109.25   $109.30  
  Purchase #5 $35.88   6.121%   $38.0762   $38.08   $38.10   $38.10  
  Purchase #6 $236.49   3.692%   $245.2212   $245.22   $245.20   $245.20  
  Purchase #7 $37.77   5.215%   $39.7397   $39.74   $39.75   $39.70  
  7 purchase totals = $896.02       $965.2580   $965.26   $965.25   $965.30