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 $238.33   3.220%   $246.0042   $246.00   $246.00   $246.00  
  Purchase #2 $248.93   7.325%   $267.1641   $267.16   $267.15   $267.20  
  Purchase #3 $216.28   13.421%   $245.3069   $245.31   $245.30   $245.30  
  Purchase #4 $199.57   5.579%   $210.704   $210.70   $210.70   $210.70  
  Purchase #5 $157.75   7.187%   $169.0875   $169.09   $169.10   $169.10  
  Purchase #6 $214.44   5.598%   $226.4444   $226.44   $226.45   $226.40  
  Purchase #7 $236.45   12.403%   $265.7769   $265.78   $265.80   $265.80  
  7 purchase totals = $1,511.75       $1,630.4880   $1,630.48   $1,630.50   $1,630.50