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 $141.56   11.801%   $158.2655   $158.27   $158.25   $158.30  
  Purchase #2 $67.41   10.855%   $74.7274   $74.73   $74.75   $74.70  
  Purchase #3 $141.70   4.314%   $147.8129   $147.81   $147.80   $147.80  
  Purchase #4 $226.79   5.610%   $239.5129   $239.51   $239.50   $239.50  
  Purchase #5 $162.50   8.108%   $175.6755   $175.68   $175.70   $175.70  
  Purchase #6 $78.53   4.233%   $81.8542   $81.85   $81.85   $81.90  
  Purchase #7 $135.65   9.843%   $149.002   $149.00   $149.00   $149.00  
  7 purchase totals = $954.14       $1,026.8504   $1,026.85   $1,026.85   $1,026.90