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 $71.68   6.661%   $76.4546   $76.45   $76.45   $76.50  
  Purchase #2 $53.43   5.593%   $56.4183   $56.42   $56.40   $56.40  
  Purchase #3 $68.56   6.196%   $72.808   $72.81   $72.80   $72.80  
  Purchase #4 $192.89   4.433%   $201.4408   $201.44   $201.45   $201.40  
  Purchase #5 $206.57   11.819%   $230.9845   $230.98   $231.00   $231.00  
  Purchase #6 $202.76   4.731%   $212.3526   $212.35   $212.35   $212.40  
  Purchase #7 $194.61   10.383%   $214.8164   $214.82   $214.80   $214.80  
  7 purchase totals = $990.50       $1,065.2752   $1,065.27   $1,065.25   $1,065.30