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 $191.93   6.621%   $204.6377   $204.64   $204.65   $204.60  
  Purchase #2 $134.59   10.782%   $149.1015   $149.10   $149.10   $149.10  
  Purchase #3 $68.25   13.847%   $77.7006   $77.70   $77.70   $77.70  
  Purchase #4 $113.76   3.615%   $117.8724   $117.87   $117.85   $117.90  
  Purchase #5 $193.37   10.285%   $213.2581   $213.26   $213.25   $213.30  
  Purchase #6 $109.77   10.572%   $121.3749   $121.37   $121.35   $121.40  
  Purchase #7 $113.39   6.418%   $120.6674   $120.67   $120.65   $120.70  
  7 purchase totals = $925.06       $1,004.6126   $1,004.61   $1,004.55   $1,004.70