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 $196.52   8.404%   $213.0355   $213.04   $213.05   $213.00  
  Purchase #2 $182.68   6.713%   $194.9433   $194.94   $194.95   $194.90  
  Purchase #3 $229.53   3.364%   $237.2514   $237.25   $237.25   $237.30  
  Purchase #4 $66.93   5.750%   $70.7785   $70.78   $70.80   $70.80  
  Purchase #5 $192.35   6.370%   $204.6027   $204.60   $204.60   $204.60  
  Purchase #6 $148.25   4.181%   $154.4483   $154.45   $154.45   $154.40  
  Purchase #7 $39.60   8.459%   $42.9498   $42.95   $42.95   $42.90  
  7 purchase totals = $1,055.86       $1,118.0095   $1,118.01   $1,118.05   $1,117.90