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 $134.98   12.458%   $151.7958   $151.80   $151.80   $151.80  
  Purchase #2 $62.26   6.678%   $66.4177   $66.42   $66.40   $66.40  
  Purchase #3 $230.73   11.379%   $256.9848   $256.98   $257.00   $257.00  
  Purchase #4 $32.28   6.128%   $34.2581   $34.26   $34.25   $34.30  
  Purchase #5 $144.85   13.561%   $164.4931   $164.49   $164.50   $164.50  
  Purchase #6 $187.51   4.387%   $195.7361   $195.74   $195.75   $195.70  
  Purchase #7 $149.56   4.861%   $156.8301   $156.83   $156.85   $156.80  
  7 purchase totals = $942.17       $1,026.5157   $1,026.52   $1,026.55   $1,026.50