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 $208.51   11.546%   $232.5846   $232.58   $232.60   $232.60  
  Purchase #2 $217.82   4.471%   $227.5587   $227.56   $227.55   $227.60  
  Purchase #3 $231.39   11.611%   $258.2567   $258.26   $258.25   $258.30  
  Purchase #4 $12.98   8.368%   $14.0662   $14.07   $14.05   $14.10  
  Purchase #5 $79.54   12.582%   $89.5477   $89.55   $89.55   $89.50  
  Purchase #6 $29.88   13.283%   $33.849   $33.85   $33.85   $33.80  
  Purchase #7 $52.84   5.419%   $55.7034   $55.70   $55.70   $55.70  
  7 purchase totals = $832.96       $911.5663   $911.57   $911.55   $911.60