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 $68.61   10.347%   $75.7091   $75.71   $75.70   $75.70  
  Purchase #2 $150.70   12.671%   $169.7952   $169.80   $169.80   $169.80  
  Purchase #3 $69.89   6.862%   $74.6859   $74.69   $74.70   $74.70  
  Purchase #4 $126.48   10.657%   $139.959   $139.96   $139.95   $140.00  
  Purchase #5 $80.43   7.134%   $86.1679   $86.17   $86.15   $86.20  
  Purchase #6 $206.25   11.686%   $230.3524   $230.35   $230.35   $230.40  
  Purchase #7 $123.55   13.344%   $140.0365   $140.04   $140.05   $140.00  
  7 purchase totals = $825.91       $916.7060   $916.72   $916.70   $916.80