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 $203.81   10.772%   $225.7644   $225.76   $225.75   $225.80  
  Purchase #2 $23.99   6.631%   $25.5808   $25.58   $25.60   $25.60  
  Purchase #3 $58.72   13.231%   $66.4892   $66.49   $66.50   $66.50  
  Purchase #4 $235.48   13.364%   $266.9495   $266.95   $266.95   $266.90  
  Purchase #5 $69.49   6.534%   $74.0305   $74.03   $74.05   $74.00  
  Purchase #6 $192.71   4.520%   $201.4205   $201.42   $201.40   $201.40  
  Purchase #7 $8.60   3.444%   $8.8962   $8.90   $8.90   $8.90  
  7 purchase totals = $792.80       $869.1311   $869.13   $869.15   $869.10