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 $148.27   11.686%   $165.5968   $165.60   $165.60   $165.60  
  Purchase #2 $244.29   10.264%   $269.3639   $269.36   $269.35   $269.40  
  Purchase #3 $205.60   4.577%   $215.0103   $215.01   $215.00   $215.00  
  Purchase #4 $161.56   9.345%   $176.6578   $176.66   $176.65   $176.70  
  Purchase #5 $11.39   7.785%   $12.2767   $12.28   $12.30   $12.30  
  Purchase #6 $72.92   6.249%   $77.4768   $77.48   $77.50   $77.50  
  Purchase #7 $66.95   4.391%   $69.8898   $69.89   $69.90   $69.90  
  7 purchase totals = $910.98       $986.2721   $986.28   $986.30   $986.40