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 $89.43   6.322%   $95.0838   $95.08   $95.10   $95.10  
  Purchase #2 $67.98   13.508%   $77.1627   $77.16   $77.15   $77.20  
  Purchase #3 $87.74   3.306%   $90.6407   $90.64   $90.65   $90.60  
  Purchase #4 $217.33   7.361%   $233.3277   $233.33   $233.35   $233.30  
  Purchase #5 $248.37   10.858%   $275.338   $275.34   $275.35   $275.30  
  Purchase #6 $188.53   13.868%   $214.6753   $214.68   $214.70   $214.70  
  Purchase #7 $247.79   7.423%   $266.1835   $266.18   $266.20   $266.20  
  7 purchase totals = $1,147.17       $1,252.4117   $1,252.41   $1,252.50   $1,252.40