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 $219.82   5.543%   $232.0046   $232.00   $232.00   $232.00  
  Purchase #2 $176.82   11.280%   $196.7653   $196.77   $196.75   $196.80  
  Purchase #3 $90.53   9.205%   $98.8633   $98.86   $98.85   $98.90  
  Purchase #4 $239.79   7.282%   $257.2515   $257.25   $257.25   $257.30  
  Purchase #5 $209.25   8.221%   $226.4524   $226.45   $226.45   $226.50  
  Purchase #6 $192.35   4.236%   $200.4979   $200.50   $200.50   $200.50  
  Purchase #7 $19.69   13.342%   $22.317   $22.32   $22.30   $22.30  
  7 purchase totals = $1,148.25       $1,234.1520   $1,234.15   $1,234.10   $1,234.30