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 $54.87   6.272%   $58.3114   $58.31   $58.30   $58.30  
  Purchase #2 $198.60   6.849%   $212.2021   $212.20   $212.20   $212.20  
  Purchase #3 $77.81   11.509%   $86.7652   $86.77   $86.75   $86.80  
  Purchase #4 $119.92   12.605%   $135.0359   $135.04   $135.05   $135.00  
  Purchase #5 $106.77   4.817%   $111.9131   $111.91   $111.90   $111.90  
  Purchase #6 $160.96   7.232%   $172.6006   $172.60   $172.60   $172.60  
  Purchase #7 $32.84   7.279%   $35.2304   $35.23   $35.25   $35.20  
  7 purchase totals = $751.77       $812.0587   $812.06   $812.05   $812.00