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 $46.28   9.690%   $50.7645   $50.76   $50.75   $50.80  
  Purchase #2 $118.47   5.389%   $124.8543   $124.85   $124.85   $124.90  
  Purchase #3 $206.80   7.866%   $223.0669   $223.07   $223.05   $223.10  
  Purchase #4 $219.70   5.178%   $231.0761   $231.08   $231.10   $231.10  
  Purchase #5 $239.60   7.352%   $257.2154   $257.22   $257.20   $257.20  
  Purchase #6 $38.45   7.304%   $41.2584   $41.26   $41.25   $41.30  
  Purchase #7 $234.87   9.200%   $256.478   $256.48   $256.50   $256.50  
  7 purchase totals = $1,104.17       $1,184.7136   $1,184.72   $1,184.70   $1,184.90