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 $164.35   8.198%   $177.8234   $177.82   $177.80   $177.80  
  Purchase #2 $121.64   11.547%   $135.6858   $135.69   $135.70   $135.70  
  Purchase #3 $111.25   10.394%   $122.8133   $122.81   $122.80   $122.80  
  Purchase #4 $160.88   4.676%   $168.4027   $168.40   $168.40   $168.40  
  Purchase #5 $56.62   6.535%   $60.3201   $60.32   $60.30   $60.30  
  Purchase #6 $126.51   13.836%   $144.0139   $144.01   $144.00   $144.00  
  Purchase #7 $198.82   3.332%   $205.4447   $205.44   $205.45   $205.40  
  7 purchase totals = $940.07       $1,014.5039   $1,014.49   $1,014.45   $1,014.40