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 $178.73   8.721%   $194.317   $194.32   $194.30   $194.30  
  Purchase #2 $75.92   8.333%   $82.2464   $82.25   $82.25   $82.20  
  Purchase #3 $207.96   9.436%   $227.5831   $227.58   $227.60   $227.60  
  Purchase #4 $161.27   9.359%   $176.3633   $176.36   $176.35   $176.40  
  Purchase #5 $159.37   6.292%   $169.3976   $169.40   $169.40   $169.40  
  Purchase #6 $39.67   12.637%   $44.6831   $44.68   $44.70   $44.70  
  Purchase #7 $172.89   12.423%   $194.3681   $194.37   $194.35   $194.40  
  7 purchase totals = $995.81       $1,088.9586   $1,088.96   $1,088.95   $1,089.00