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 $78.88   5.675%   $83.3564   $83.36   $83.35   $83.40  
  Purchase #2 $241.89   11.291%   $269.2018   $269.20   $269.20   $269.20  
  Purchase #3 $207.87   7.442%   $223.3397   $223.34   $223.35   $223.30  
  Purchase #4 $157.92   11.725%   $176.4361   $176.44   $176.45   $176.40  
  Purchase #5 $132.44   8.602%   $143.8325   $143.83   $143.85   $143.80  
  Purchase #6 $65.87   3.633%   $68.2631   $68.26   $68.25   $68.30  
  Purchase #7 $231.49   6.125%   $245.6688   $245.67   $245.65   $245.70  
  7 purchase totals = $1,116.36       $1,210.0984   $1,210.10   $1,210.10   $1,210.10