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 $88.35   8.835%   $96.1557   $96.16   $96.15   $96.20  
  Purchase #2 $185.49   4.238%   $193.3511   $193.35   $193.35   $193.40  
  Purchase #3 $156.93   3.620%   $162.6109   $162.61   $162.60   $162.60  
  Purchase #4 $169.36   9.825%   $185.9996   $186.00   $186.00   $186.00  
  Purchase #5 $27.70   5.372%   $29.188   $29.19   $29.20   $29.20  
  Purchase #6 $24.61   5.177%   $25.8841   $25.88   $25.90   $25.90  
  Purchase #7 $156.71   11.363%   $174.517   $174.52   $174.50   $174.50  
  7 purchase totals = $809.15       $867.7064   $867.71   $867.70   $867.80