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 $162.99   6.861%   $174.1727   $174.17   $174.15   $174.20  
  Purchase #2 $81.94   13.294%   $92.8331   $92.83   $92.85   $92.80  
  Purchase #3 $70.61   9.833%   $77.5531   $77.55   $77.55   $77.60  
  Purchase #4 $150.26   10.675%   $166.3003   $166.30   $166.30   $166.30  
  Purchase #5 $232.44   3.600%   $240.8078   $240.81   $240.80   $240.80  
  Purchase #6 $21.89   12.852%   $24.7033   $24.70   $24.70   $24.70  
  Purchase #7 $217.52   8.676%   $236.392   $236.39   $236.40   $236.40  
  7 purchase totals = $937.65       $1,012.7623   $1,012.75   $1,012.75   $1,012.80