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 $87.46   10.393%   $96.5497   $96.55   $96.55   $96.50  
  Purchase #2 $77.56   10.343%   $85.582   $85.58   $85.60   $85.60  
  Purchase #3 $131.31   4.223%   $136.8552   $136.86   $136.85   $136.90  
  Purchase #4 $210.78   4.601%   $220.478   $220.48   $220.50   $220.50  
  Purchase #5 $105.65   8.565%   $114.6989   $114.70   $114.70   $114.70  
  Purchase #6 $151.26   8.206%   $163.6724   $163.67   $163.65   $163.70  
  Purchase #7 $106.39   7.151%   $113.9979   $114.00   $114.00   $114.00  
  7 purchase totals = $870.41       $931.8341   $931.84   $931.85   $931.90