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 $197.93   5.569%   $208.9527   $208.95   $208.95   $209.00  
  Purchase #2 $153.85   7.811%   $165.8672   $165.87   $165.85   $165.90  
  Purchase #3 $20.92   11.337%   $23.2917   $23.29   $23.30   $23.30  
  Purchase #4 $182.42   4.781%   $191.1415   $191.14   $191.15   $191.10  
  Purchase #5 $181.83   6.820%   $194.2308   $194.23   $194.25   $194.20  
  Purchase #6 $243.51   10.737%   $269.6557   $269.66   $269.65   $269.70  
  Purchase #7 $219.41   11.348%   $244.3086   $244.31   $244.30   $244.30  
  7 purchase totals = $1,199.87       $1,297.4482   $1,297.45   $1,297.45   $1,297.50