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 $54.90   11.630%   $61.2849   $61.28   $61.30   $61.30  
  Purchase #2 $196.56   7.513%   $211.3276   $211.33   $211.35   $211.30  
  Purchase #3 $155.27   7.596%   $167.0643   $167.06   $167.05   $167.10  
  Purchase #4 $182.85   11.861%   $204.5378   $204.54   $204.55   $204.50  
  Purchase #5 $211.95   3.237%   $218.8108   $218.81   $218.80   $218.80  
  Purchase #6 $14.25   4.560%   $14.8998   $14.90   $14.90   $14.90  
  Purchase #7 $16.52   9.661%   $18.116   $18.12   $18.10   $18.10  
  7 purchase totals = $832.30       $896.0412   $896.04   $896.05   $896.00