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 $154.60   10.614%   $171.0092   $171.01   $171.00   $171.00  
  Purchase #2 $224.42   12.717%   $252.9595   $252.96   $252.95   $253.00  
  Purchase #3 $161.41   5.235%   $169.8598   $169.86   $169.85   $169.90  
  Purchase #4 $106.87   8.511%   $115.9657   $115.97   $115.95   $116.00  
  Purchase #5 $54.53   12.471%   $61.3304   $61.33   $61.35   $61.30  
  Purchase #6 $183.98   13.247%   $208.3518   $208.35   $208.35   $208.40  
  Purchase #7 $235.86   6.176%   $250.4267   $250.43   $250.45   $250.40  
  7 purchase totals = $1,121.67       $1,229.9031   $1,229.91   $1,229.90   $1,230.00