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 $56.52   9.209%   $61.7249   $61.72   $61.70   $61.70  
  Purchase #2 $118.86   7.711%   $128.0253   $128.03   $128.05   $128.00  
  Purchase #3 $242.76   9.492%   $265.8028   $265.80   $265.80   $265.80  
  Purchase #4 $98.78   6.801%   $105.498   $105.50   $105.50   $105.50  
  Purchase #5 $233.98   3.458%   $242.071   $242.07   $242.05   $242.10  
  Purchase #6 $11.32   5.690%   $11.9641   $11.96   $11.95   $12.00  
  Purchase #7 $65.31   8.703%   $70.9939   $70.99   $71.00   $71.00  
  7 purchase totals = $827.53       $886.0800   $886.07   $886.05   $886.10