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 $160.65   8.699%   $174.6249   $174.62   $174.60   $174.60  
  Purchase #2 $173.87   13.706%   $197.7006   $197.70   $197.70   $197.70  
  Purchase #3 $71.25   11.304%   $79.3041   $79.30   $79.30   $79.30  
  Purchase #4 $194.57   8.551%   $211.2077   $211.21   $211.20   $211.20  
  Purchase #5 $54.97   10.229%   $60.5929   $60.59   $60.60   $60.60  
  Purchase #6 $54.70   5.477%   $57.6959   $57.70   $57.70   $57.70  
  Purchase #7 $245.49   9.641%   $269.1577   $269.16   $269.15   $269.20  
  7 purchase totals = $955.50       $1,050.2838   $1,050.28   $1,050.25   $1,050.30