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 $72.92   3.416%   $75.4109   $75.41   $75.40   $75.40  
  Purchase #2 $175.94   12.318%   $197.6123   $197.61   $197.60   $197.60  
  Purchase #3 $9.65   7.683%   $10.3914   $10.39   $10.40   $10.40  
  Purchase #4 $106.79   13.536%   $121.2451   $121.25   $121.25   $121.20  
  Purchase #5 $183.51   6.752%   $195.9006   $195.90   $195.90   $195.90  
  Purchase #6 $69.93   3.516%   $72.3887   $72.39   $72.40   $72.40  
  Purchase #7 $57.55   7.511%   $61.8726   $61.87   $61.85   $61.90  
  7 purchase totals = $676.29       $734.8216   $734.82   $734.80   $734.80