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 $238.71   9.452%   $261.2729   $261.27   $261.25   $261.30  
  Purchase #2 $227.88   8.112%   $246.3656   $246.37   $246.35   $246.40  
  Purchase #3 $129.29   3.710%   $134.0867   $134.09   $134.10   $134.10  
  Purchase #4 $65.35   13.209%   $73.9821   $73.98   $74.00   $74.00  
  Purchase #5 $121.76   10.429%   $134.4584   $134.46   $134.45   $134.50  
  Purchase #6 $86.31   11.567%   $96.2935   $96.29   $96.30   $96.30  
  Purchase #7 $165.82   11.647%   $185.1331   $185.13   $185.15   $185.10  
  7 purchase totals = $1,035.12       $1,131.5923   $1,131.59   $1,131.60   $1,131.70