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 $234.89   10.563%   $259.7014   $259.70   $259.70   $259.70  
  Purchase #2 $41.95   4.178%   $43.7027   $43.70   $43.70   $43.70  
  Purchase #3 $181.60   10.385%   $200.4592   $200.46   $200.45   $200.50  
  Purchase #4 $128.63   8.747%   $139.8813   $139.88   $139.90   $139.90  
  Purchase #5 $194.30   4.482%   $203.0085   $203.01   $203.00   $203.00  
  Purchase #6 $235.36   4.739%   $246.5137   $246.51   $246.50   $246.50  
  Purchase #7 $193.40   7.608%   $208.1139   $208.11   $208.10   $208.10  
  7 purchase totals = $1,210.13       $1,301.3807   $1,301.37   $1,301.35   $1,301.40