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 $77.96   12.426%   $87.6473   $87.65   $87.65   $87.60  
  Purchase #2 $117.96   12.349%   $132.5269   $132.53   $132.55   $132.50  
  Purchase #3 $87.81   8.837%   $95.5698   $95.57   $95.55   $95.60  
  Purchase #4 $30.94   3.644%   $32.0675   $32.07   $32.05   $32.10  
  Purchase #5 $99.87   12.578%   $112.4316   $112.43   $112.45   $112.40  
  Purchase #6 $206.74   10.136%   $227.6952   $227.70   $227.70   $227.70  
  Purchase #7 $175.79   5.296%   $185.0998   $185.10   $185.10   $185.10  
  7 purchase totals = $797.07       $873.0381   $873.05   $873.05   $873.00