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 $67.71   4.729%   $70.912   $70.91   $70.90   $70.90  
  Purchase #2 $113.29   4.464%   $118.3473   $118.35   $118.35   $118.30  
  Purchase #3 $165.63   6.294%   $176.0548   $176.05   $176.05   $176.10  
  Purchase #4 $105.93   13.310%   $120.0293   $120.03   $120.05   $120.00  
  Purchase #5 $176.52   3.250%   $182.2569   $182.26   $182.25   $182.30  
  Purchase #6 $38.30   5.248%   $40.31   $40.31   $40.30   $40.30  
  Purchase #7 $165.41   5.508%   $174.5208   $174.52   $174.50   $174.50  
  7 purchase totals = $832.79       $882.4311   $882.43   $882.40   $882.40