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 $194.61   13.217%   $220.3316   $220.33   $220.35   $220.30  
  Purchase #2 $248.30   12.175%   $278.5305   $278.53   $278.55   $278.50  
  Purchase #3 $164.83   9.801%   $180.985   $180.99   $181.00   $181.00  
  Purchase #4 $128.69   5.826%   $136.1875   $136.19   $136.20   $136.20  
  Purchase #5 $205.67   8.195%   $222.5247   $222.52   $222.50   $222.50  
  Purchase #6 $61.62   12.583%   $69.3736   $69.37   $69.35   $69.40  
  Purchase #7 $238.94   3.373%   $246.9994   $247.00   $247.00   $247.00  
  7 purchase totals = $1,242.66       $1,354.9323   $1,354.93   $1,354.95   $1,354.90