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 $213.83   9.569%   $234.2914   $234.29   $234.30   $234.30  
  Purchase #2 $131.73   11.593%   $147.0015   $147.00   $147.00   $147.00  
  Purchase #3 $180.47   12.739%   $203.4601   $203.46   $203.45   $203.50  
  Purchase #4 $181.72   13.777%   $206.7556   $206.76   $206.75   $206.80  
  Purchase #5 $64.37   7.232%   $69.0252   $69.03   $69.05   $69.00  
  Purchase #6 $215.53   11.398%   $240.0961   $240.10   $240.10   $240.10  
  Purchase #7 $154.97   3.202%   $159.9321   $159.93   $159.95   $159.90  
  7 purchase totals = $1,142.62       $1,260.5620   $1,260.57   $1,260.60   $1,260.60