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 $206.25   8.484%   $223.7483   $223.75   $223.75   $223.70  
  Purchase #2 $82.41   6.816%   $88.0271   $88.03   $88.05   $88.00  
  Purchase #3 $248.42   8.573%   $269.717   $269.72   $269.70   $269.70  
  Purchase #4 $90.76   9.455%   $99.3414   $99.34   $99.35   $99.30  
  Purchase #5 $150.58   12.429%   $169.2956   $169.30   $169.30   $169.30  
  Purchase #6 $136.76   10.625%   $151.2908   $151.29   $151.30   $151.30  
  Purchase #7 $77.59   8.583%   $84.2495   $84.25   $84.25   $84.20  
  7 purchase totals = $992.77       $1,085.6697   $1,085.68   $1,085.70   $1,085.50