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 $239.65   5.295%   $252.3395   $252.34   $252.35   $252.30  
  Purchase #2 $64.37   10.659%   $71.2312   $71.23   $71.25   $71.20  
  Purchase #3 $35.66   10.871%   $39.5366   $39.54   $39.55   $39.50  
  Purchase #4 $69.40   6.385%   $73.8312   $73.83   $73.85   $73.80  
  Purchase #5 $132.92   7.628%   $143.0591   $143.06   $143.05   $143.10  
  Purchase #6 $186.65   3.404%   $193.0036   $193.00   $193.00   $193.00  
  Purchase #7 $149.85   12.341%   $168.343   $168.34   $168.35   $168.30  
  7 purchase totals = $878.50       $941.3442   $941.34   $941.40   $941.20