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 $24.66   7.783%   $26.5793   $26.58   $26.60   $26.60  
  Purchase #2 $222.98   8.671%   $242.3146   $242.31   $242.30   $242.30  
  Purchase #3 $160.70   4.770%   $168.3654   $168.37   $168.35   $168.40  
  Purchase #4 $225.92   5.723%   $238.8494   $238.85   $238.85   $238.80  
  Purchase #5 $36.85   13.279%   $41.7433   $41.74   $41.75   $41.70  
  Purchase #6 $205.33   12.232%   $230.446   $230.45   $230.45   $230.40  
  Purchase #7 $41.65   5.422%   $43.9083   $43.91   $43.90   $43.90  
  7 purchase totals = $918.09       $992.2063   $992.21   $992.20   $992.10