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 $168.74   13.199%   $191.012   $191.01   $191.00   $191.00  
  Purchase #2 $169.32   9.827%   $185.9591   $185.96   $185.95   $186.00  
  Purchase #3 $10.89   13.332%   $12.3419   $12.34   $12.35   $12.30  
  Purchase #4 $109.44   7.323%   $117.4543   $117.45   $117.45   $117.50  
  Purchase #5 $184.52   13.704%   $209.8066   $209.81   $209.80   $209.80  
  Purchase #6 $136.54   11.577%   $152.3472   $152.35   $152.35   $152.30  
  Purchase #7 $105.76   13.170%   $119.6886   $119.69   $119.70   $119.70  
  7 purchase totals = $885.21       $988.6097   $988.61   $988.60   $988.60