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 $250.27   13.702%   $284.562   $284.56   $284.55   $284.60  
  Purchase #2 $67.54   9.114%   $73.6956   $73.70   $73.70   $73.70  
  Purchase #3 $231.49   9.239%   $252.8774   $252.88   $252.90   $252.90  
  Purchase #4 $81.76   12.550%   $92.0209   $92.02   $92.00   $92.00  
  Purchase #5 $6.61   10.438%   $7.3   $7.30   $7.30   $7.30  
  Purchase #6 $130.28   11.310%   $145.0147   $145.01   $145.00   $145.00  
  Purchase #7 $203.78   13.767%   $231.8344   $231.83   $231.85   $231.80  
  7 purchase totals = $971.73       $1,087.3050   $1,087.30   $1,087.30   $1,087.30