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 $53.78   8.697%   $58.4572   $58.46   $58.45   $58.50  
  Purchase #2 $64.60   13.337%   $73.2157   $73.22   $73.20   $73.20  
  Purchase #3 $155.72   3.513%   $161.1904   $161.19   $161.20   $161.20  
  Purchase #4 $63.46   3.510%   $65.6874   $65.69   $65.70   $65.70  
  Purchase #5 $218.80   12.774%   $246.7495   $246.75   $246.75   $246.70  
  Purchase #6 $206.83   3.788%   $214.6647   $214.66   $214.65   $214.70  
  Purchase #7 $174.85   3.869%   $181.6149   $181.61   $181.60   $181.60  
  7 purchase totals = $938.04       $1,001.5798   $1,001.58   $1,001.55   $1,001.60