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 $141.34   9.458%   $154.7079   $154.71   $154.70   $154.70  
  Purchase #2 $181.64   5.787%   $192.1515   $192.15   $192.15   $192.20  
  Purchase #3 $85.88   4.618%   $89.8459   $89.85   $89.85   $89.80  
  Purchase #4 $207.33   10.437%   $228.969   $228.97   $228.95   $229.00  
  Purchase #5 $131.55   3.122%   $135.657   $135.66   $135.65   $135.70  
  Purchase #6 $196.96   4.737%   $206.29   $206.29   $206.30   $206.30  
  Purchase #7 $241.40   4.831%   $253.062   $253.06   $253.05   $253.10  
  7 purchase totals = $1,186.10       $1,260.6833   $1,260.69   $1,260.65   $1,260.80