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 $32.47   10.747%   $35.9596   $35.96   $35.95   $36.00  
  Purchase #2 $139.77   11.160%   $155.3683   $155.37   $155.35   $155.40  
  Purchase #3 $212.72   12.816%   $239.9822   $239.98   $240.00   $240.00  
  Purchase #4 $181.75   3.737%   $188.542   $188.54   $188.55   $188.50  
  Purchase #5 $149.58   13.402%   $169.6267   $169.63   $169.65   $169.60  
  Purchase #6 $111.32   4.127%   $115.9142   $115.91   $115.90   $115.90  
  Purchase #7 $158.88   6.253%   $168.8148   $168.81   $168.80   $168.80  
  7 purchase totals = $986.49       $1,074.2078   $1,074.20   $1,074.20   $1,074.20