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 $68.73   12.833%   $77.5501   $77.55   $77.55   $77.60  
  Purchase #2 $103.44   3.612%   $107.1763   $107.18   $107.20   $107.20  
  Purchase #3 $241.98   8.667%   $262.9524   $262.95   $262.95   $263.00  
  Purchase #4 $177.59   11.361%   $197.766   $197.77   $197.75   $197.80  
  Purchase #5 $40.79   6.232%   $43.332   $43.33   $43.35   $43.30  
  Purchase #6 $231.68   3.192%   $239.0752   $239.08   $239.10   $239.10  
  Purchase #7 $20.83   5.478%   $21.9711   $21.97   $21.95   $22.00  
  7 purchase totals = $885.04       $949.8231   $949.83   $949.85   $950.00