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 $47.82   9.843%   $52.5269   $52.53   $52.55   $52.50  
  Purchase #2 $124.69   4.564%   $130.3809   $130.38   $130.40   $130.40  
  Purchase #3 $74.81   10.254%   $82.481   $82.48   $82.50   $82.50  
  Purchase #4 $162.77   10.186%   $179.3498   $179.35   $179.35   $179.30  
  Purchase #5 $128.47   11.658%   $143.447   $143.45   $143.45   $143.40  
  Purchase #6 $28.53   13.379%   $32.347   $32.35   $32.35   $32.30  
  Purchase #7 $128.32   10.426%   $141.6986   $141.70   $141.70   $141.70  
  7 purchase totals = $695.41       $762.2312   $762.24   $762.30   $762.10