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 $68.92   13.782%   $78.4186   $78.42   $78.40   $78.40  
  Purchase #2 $164.58   4.688%   $172.2955   $172.30   $172.30   $172.30  
  Purchase #3 $155.49   13.814%   $176.9694   $176.97   $176.95   $177.00  
  Purchase #4 $233.74   6.464%   $248.849   $248.85   $248.85   $248.80  
  Purchase #5 $242.80   7.300%   $260.5244   $260.52   $260.50   $260.50  
  Purchase #6 $185.74   13.809%   $211.3888   $211.39   $211.40   $211.40  
  Purchase #7 $216.37   8.803%   $235.4171   $235.42   $235.40   $235.40  
  7 purchase totals = $1,267.64       $1,383.8628   $1,383.87   $1,383.80   $1,383.80