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 $192.53   3.278%   $198.8411   $198.84   $198.85   $198.80  
  Purchase #2 $150.98   9.511%   $165.3397   $165.34   $165.35   $165.30  
  Purchase #3 $118.45   5.252%   $124.671   $124.67   $124.65   $124.70  
  Purchase #4 $244.55   6.388%   $260.1719   $260.17   $260.15   $260.20  
  Purchase #5 $18.36   4.282%   $19.1462   $19.15   $19.15   $19.10  
  Purchase #6 $113.58   12.366%   $127.6253   $127.63   $127.65   $127.60  
  Purchase #7 $118.91   6.621%   $126.783   $126.78   $126.80   $126.80  
  7 purchase totals = $957.36       $1,022.5782   $1,022.58   $1,022.60   $1,022.50