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 $161.83   3.531%   $167.5442   $167.54   $167.55   $167.50  
  Purchase #2 $152.28   5.295%   $160.3432   $160.34   $160.35   $160.30  
  Purchase #3 $23.72   11.248%   $26.388   $26.39   $26.40   $26.40  
  Purchase #4 $11.42   5.266%   $12.0214   $12.02   $12.00   $12.00  
  Purchase #5 $105.66   3.360%   $109.2102   $109.21   $109.20   $109.20  
  Purchase #6 $175.47   9.674%   $192.445   $192.45   $192.45   $192.40  
  Purchase #7 $196.70   5.236%   $206.9992   $207.00   $207.00   $207.00  
  7 purchase totals = $827.08       $874.9512   $874.95   $874.95   $874.80