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 $222.85   8.183%   $241.0858   $241.09   $241.10   $241.10  
  Purchase #2 $41.79   4.402%   $43.6296   $43.63   $43.65   $43.60  
  Purchase #3 $154.29   7.155%   $165.3294   $165.33   $165.35   $165.30  
  Purchase #4 $206.27   4.116%   $214.7601   $214.76   $214.75   $214.80  
  Purchase #5 $238.41   5.266%   $250.9647   $250.96   $250.95   $251.00  
  Purchase #6 $165.71   11.293%   $184.4236   $184.42   $184.40   $184.40  
  Purchase #7 $65.35   8.179%   $70.695   $70.70   $70.70   $70.70  
  7 purchase totals = $1,094.67       $1,170.8882   $1,170.89   $1,170.90   $1,170.90