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 $221.43   6.435%   $235.679   $235.68   $235.70   $235.70  
  Purchase #2 $196.28   10.270%   $216.438   $216.44   $216.45   $216.40  
  Purchase #3 $10.95   11.602%   $12.2204   $12.22   $12.20   $12.20  
  Purchase #4 $46.93   8.321%   $50.835   $50.84   $50.85   $50.80  
  Purchase #5 $211.65   10.244%   $233.3314   $233.33   $233.35   $233.30  
  Purchase #6 $7.45   12.309%   $8.367   $8.37   $8.35   $8.40  
  Purchase #7 $101.84   6.432%   $108.3903   $108.39   $108.40   $108.40  
  7 purchase totals = $796.53       $865.2611   $865.27   $865.30   $865.20