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 $53.89   4.601%   $56.3695   $56.37   $56.35   $56.40  
  Purchase #2 $151.96   10.807%   $168.3823   $168.38   $168.40   $168.40  
  Purchase #3 $24.49   4.741%   $25.6511   $25.65   $25.65   $25.70  
  Purchase #4 $123.84   6.789%   $132.2475   $132.25   $132.25   $132.20  
  Purchase #5 $54.76   6.538%   $58.3402   $58.34   $58.35   $58.30  
  Purchase #6 $179.48   6.424%   $191.0098   $191.01   $191.00   $191.00  
  Purchase #7 $154.43   11.242%   $171.791   $171.79   $171.80   $171.80  
  7 purchase totals = $742.85       $803.7914   $803.79   $803.80   $803.80