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 $82.79   3.694%   $85.8483   $85.85   $85.85   $85.80  
  Purchase #2 $50.77   13.127%   $57.4346   $57.43   $57.45   $57.40  
  Purchase #3 $27.68   7.198%   $29.6724   $29.67   $29.65   $29.70  
  Purchase #4 $86.31   12.635%   $97.2153   $97.22   $97.20   $97.20  
  Purchase #5 $183.59   9.778%   $201.5414   $201.54   $201.55   $201.50  
  Purchase #6 $80.81   12.321%   $90.7666   $90.77   $90.75   $90.80  
  Purchase #7 $227.50   7.373%   $244.2736   $244.27   $244.25   $244.30  
  7 purchase totals = $739.45       $806.7522   $806.75   $806.70   $806.70