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 $26.95   9.807%   $29.593   $29.59   $29.60   $29.60  
  Purchase #2 $90.84   4.219%   $94.6725   $94.67   $94.65   $94.70  
  Purchase #3 $117.65   3.534%   $121.8078   $121.81   $121.80   $121.80  
  Purchase #4 $220.76   5.538%   $232.9857   $232.99   $233.00   $233.00  
  Purchase #5 $172.65   7.238%   $185.1464   $185.15   $185.15   $185.10  
  Purchase #6 $235.84   12.734%   $265.8719   $265.87   $265.85   $265.90  
  Purchase #7 $72.98   10.269%   $80.4743   $80.47   $80.45   $80.50  
  7 purchase totals = $937.67       $1,010.5516   $1,010.55   $1,010.50   $1,010.60