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 $235.96   13.298%   $267.338   $267.34   $267.35   $267.30  
  Purchase #2 $169.33   6.664%   $180.6142   $180.61   $180.60   $180.60  
  Purchase #3 $241.45   12.119%   $270.7113   $270.71   $270.70   $270.70  
  Purchase #4 $67.72   10.130%   $74.58   $74.58   $74.60   $74.60  
  Purchase #5 $181.53   8.231%   $196.4717   $196.47   $196.45   $196.50  
  Purchase #6 $227.77   7.719%   $245.3516   $245.35   $245.35   $245.40  
  Purchase #7 $22.65   11.161%   $25.178   $25.18   $25.20   $25.20  
  7 purchase totals = $1,146.41       $1,260.2448   $1,260.24   $1,260.25   $1,260.30