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 $62.42   7.396%   $67.0366   $67.04   $67.05   $67.00  
  Purchase #2 $10.99   6.410%   $11.6945   $11.69   $11.70   $11.70  
  Purchase #3 $216.65   11.745%   $242.0955   $242.10   $242.10   $242.10  
  Purchase #4 $168.75   12.573%   $189.9669   $189.97   $189.95   $190.00  
  Purchase #5 $13.87   6.120%   $14.7188   $14.72   $14.70   $14.70  
  Purchase #6 $219.49   3.333%   $226.8056   $226.81   $226.80   $226.80  
  Purchase #7 $152.49   10.676%   $168.7698   $168.77   $168.75   $168.80  
  7 purchase totals = $844.66       $921.0877   $921.10   $921.05   $921.10