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 $59.62   7.524%   $64.1058   $64.11   $64.10   $64.10  
  Purchase #2 $40.83   13.154%   $46.2008   $46.20   $46.20   $46.20  
  Purchase #3 $34.42   11.157%   $38.2602   $38.26   $38.25   $38.30  
  Purchase #4 $166.25   5.651%   $175.6448   $175.64   $175.65   $175.60  
  Purchase #5 $194.47   9.251%   $212.4604   $212.46   $212.45   $212.50  
  Purchase #6 $101.59   9.276%   $111.0135   $111.01   $111.00   $111.00  
  Purchase #7 $39.58   13.196%   $44.803   $44.80   $44.80   $44.80  
  7 purchase totals = $636.76       $692.4885   $692.48   $692.45   $692.50