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 $61.39   10.223%   $67.6659   $67.67   $67.65   $67.70  
  Purchase #2 $220.94   12.358%   $248.2438   $248.24   $248.25   $248.20  
  Purchase #3 $141.82   4.294%   $147.9098   $147.91   $147.90   $147.90  
  Purchase #4 $227.83   7.697%   $245.3661   $245.37   $245.35   $245.40  
  Purchase #5 $209.66   12.216%   $235.2721   $235.27   $235.25   $235.30  
  Purchase #6 $20.37   3.511%   $21.0852   $21.09   $21.10   $21.10  
  Purchase #7 $106.95   4.761%   $112.0419   $112.04   $112.05   $112.00  
  7 purchase totals = $988.96       $1,077.5848   $1,077.59   $1,077.55   $1,077.60