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 $41.66   7.201%   $44.6599   $44.66   $44.65   $44.70  
  Purchase #2 $90.46   6.123%   $95.9989   $96.00   $96.00   $96.00  
  Purchase #3 $57.77   6.540%   $61.5482   $61.55   $61.55   $61.50  
  Purchase #4 $134.53   10.396%   $148.5157   $148.52   $148.50   $148.50  
  Purchase #5 $175.27   8.678%   $190.4799   $190.48   $190.50   $190.50  
  Purchase #6 $143.57   5.359%   $151.2639   $151.26   $151.25   $151.30  
  Purchase #7 $197.82   11.233%   $220.0411   $220.04   $220.05   $220.00  
  7 purchase totals = $841.08       $912.5076   $912.51   $912.50   $912.50