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 $236.85   3.539%   $245.2321   $245.23   $245.25   $245.20  
  Purchase #2 $150.35   10.128%   $165.5774   $165.58   $165.60   $165.60  
  Purchase #3 $42.26   13.670%   $48.0369   $48.04   $48.05   $48.00  
  Purchase #4 $200.37   12.817%   $226.0514   $226.05   $226.05   $226.10  
  Purchase #5 $61.44   8.255%   $66.5119   $66.51   $66.50   $66.50  
  Purchase #6 $72.80   3.702%   $75.4951   $75.50   $75.50   $75.50  
  Purchase #7 $248.77   10.285%   $274.356   $274.36   $274.35   $274.40  
  7 purchase totals = $1,012.84       $1,101.2608   $1,101.27   $1,101.30   $1,101.30