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 $84.93   8.711%   $92.3283   $92.33   $92.35   $92.30  
  Purchase #2 $132.43   13.576%   $150.4087   $150.41   $150.40   $150.40  
  Purchase #3 $211.97   7.772%   $228.4443   $228.44   $228.45   $228.40  
  Purchase #4 $199.30   4.567%   $208.402   $208.40   $208.40   $208.40  
  Purchase #5 $179.68   13.299%   $203.5756   $203.58   $203.60   $203.60  
  Purchase #6 $173.75   5.495%   $183.2976   $183.30   $183.30   $183.30  
  Purchase #7 $165.50   4.152%   $172.3716   $172.37   $172.35   $172.40  
  7 purchase totals = $1,147.56       $1,238.8281   $1,238.83   $1,238.85   $1,238.80