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 $57.45   10.163%   $63.2886   $63.29   $63.30   $63.30  
  Purchase #2 $94.59   12.822%   $106.7183   $106.72   $106.70   $106.70  
  Purchase #3 $38.91   12.830%   $43.9022   $43.90   $43.90   $43.90  
  Purchase #4 $227.94   6.768%   $243.367   $243.37   $243.35   $243.40  
  Purchase #5 $11.75   6.340%   $12.495   $12.50   $12.50   $12.50  
  Purchase #6 $141.78   9.103%   $154.6862   $154.69   $154.70   $154.70  
  Purchase #7 $182.77   13.366%   $207.199   $207.20   $207.20   $207.20  
  7 purchase totals = $755.19       $831.6563   $831.67   $831.65   $831.70