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 $61.77   6.133%   $65.5584   $65.56   $65.55   $65.60  
  Purchase #2 $12.93   13.161%   $14.6317   $14.63   $14.65   $14.60  
  Purchase #3 $45.65   8.334%   $49.4545   $49.45   $49.45   $49.50  
  Purchase #4 $103.48   13.215%   $117.1549   $117.15   $117.15   $117.20  
  Purchase #5 $217.65   6.582%   $231.9757   $231.98   $232.00   $232.00  
  Purchase #6 $172.90   5.581%   $182.5495   $182.55   $182.55   $182.50  
  Purchase #7 $154.75   12.608%   $174.2609   $174.26   $174.25   $174.30  
  7 purchase totals = $769.13       $835.5856   $835.58   $835.60   $835.70