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 $53.83   7.129%   $57.6675   $57.67   $57.65   $57.70  
  Purchase #2 $120.75   7.675%   $130.0176   $130.02   $130.00   $130.00  
  Purchase #3 $198.63   12.218%   $222.8986   $222.90   $222.90   $222.90  
  Purchase #4 $69.61   4.295%   $72.5997   $72.60   $72.60   $72.60  
  Purchase #5 $156.63   11.112%   $174.0347   $174.03   $174.05   $174.00  
  Purchase #6 $210.94   6.529%   $224.7123   $224.71   $224.70   $224.70  
  Purchase #7 $56.51   3.799%   $58.6568   $58.66   $58.65   $58.70  
  7 purchase totals = $866.90       $940.5872   $940.59   $940.55   $940.60