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 $136.68   10.487%   $151.0136   $151.01   $151.00   $151.00  
  Purchase #2 $247.81   10.729%   $274.3975   $274.40   $274.40   $274.40  
  Purchase #3 $53.82   13.205%   $60.9269   $60.93   $60.95   $60.90  
  Purchase #4 $116.74   6.283%   $124.0748   $124.07   $124.05   $124.10  
  Purchase #5 $13.42   7.547%   $14.4328   $14.43   $14.45   $14.40  
  Purchase #6 $228.31   10.693%   $252.7232   $252.72   $252.70   $252.70  
  Purchase #7 $14.99   6.846%   $16.0162   $16.02   $16.00   $16.00  
  7 purchase totals = $811.77       $893.5850   $893.58   $893.55   $893.50