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 $55.58   10.148%   $61.2203   $61.22   $61.20   $61.20  
  Purchase #2 $179.83   7.835%   $193.9197   $193.92   $193.90   $193.90  
  Purchase #3 $136.37   4.717%   $142.8026   $142.80   $142.80   $142.80  
  Purchase #4 $91.65   11.313%   $102.0184   $102.02   $102.00   $102.00  
  Purchase #5 $32.99   13.853%   $37.5601   $37.56   $37.55   $37.60  
  Purchase #6 $21.25   9.364%   $23.2399   $23.24   $23.25   $23.20  
  Purchase #7 $142.62   6.403%   $151.752   $151.75   $151.75   $151.80  
  7 purchase totals = $660.29       $712.5130   $712.51   $712.45   $712.50