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 $58.41   6.135%   $61.9935   $61.99   $62.00   $62.00  
  Purchase #2 $134.76   13.117%   $152.4365   $152.44   $152.45   $152.40  
  Purchase #3 $226.86   3.735%   $235.3332   $235.33   $235.35   $235.30  
  Purchase #4 $40.52   6.446%   $43.1319   $43.13   $43.15   $43.10  
  Purchase #5 $67.91   7.623%   $73.0868   $73.09   $73.10   $73.10  
  Purchase #6 $153.26   9.363%   $167.6097   $167.61   $167.60   $167.60  
  Purchase #7 $36.58   9.427%   $40.0284   $40.03   $40.05   $40.00  
  7 purchase totals = $718.30       $773.6200   $773.62   $773.70   $773.50