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 $24.25   9.692%   $26.6003   $26.60   $26.60   $26.60  
  Purchase #2 $88.78   5.558%   $93.7144   $93.71   $93.70   $93.70  
  Purchase #3 $92.78   9.245%   $101.3575   $101.36   $101.35   $101.40  
  Purchase #4 $161.54   3.636%   $167.4136   $167.41   $167.40   $167.40  
  Purchase #5 $134.94   9.183%   $147.3315   $147.33   $147.35   $147.30  
  Purchase #6 $73.41   10.504%   $81.121   $81.12   $81.10   $81.10  
  Purchase #7 $116.48   8.421%   $126.2888   $126.29   $126.30   $126.30  
  7 purchase totals = $692.18       $743.8271   $743.82   $743.80   $743.80