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 $213.32   10.161%   $234.9954   $235.00   $235.00   $235.00  
  Purchase #2 $165.25   9.812%   $181.4643   $181.46   $181.45   $181.50  
  Purchase #3 $221.86   10.711%   $245.6234   $245.62   $245.60   $245.60  
  Purchase #4 $169.97   4.158%   $177.0374   $177.04   $177.05   $177.00  
  Purchase #5 $71.36   9.763%   $78.3269   $78.33   $78.35   $78.30  
  Purchase #6 $14.58   5.315%   $15.3549   $15.35   $15.35   $15.40  
  Purchase #7 $62.70   12.852%   $70.7582   $70.76   $70.75   $70.80  
  7 purchase totals = $919.04       $1,003.5605   $1,003.56   $1,003.55   $1,003.60