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 $75.75   13.753%   $86.1679   $86.17   $86.15   $86.20  
  Purchase #2 $169.25   12.645%   $190.6517   $190.65   $190.65   $190.70  
  Purchase #3 $213.74   10.377%   $235.9198   $235.92   $235.90   $235.90  
  Purchase #4 $193.36   8.478%   $209.7531   $209.75   $209.75   $209.80  
  Purchase #5 $142.28   8.516%   $154.3966   $154.40   $154.40   $154.40  
  Purchase #6 $55.69   4.169%   $58.0117   $58.01   $58.00   $58.00  
  Purchase #7 $209.80   3.565%   $217.2794   $217.28   $217.30   $217.30  
  7 purchase totals = $1,059.87       $1,152.1802   $1,152.18   $1,152.15   $1,152.30