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 $204.61   12.421%   $230.0246   $230.02   $230.00   $230.00  
  Purchase #2 $135.59   11.844%   $151.6493   $151.65   $151.65   $151.60  
  Purchase #3 $230.25   6.430%   $245.0551   $245.06   $245.05   $245.10  
  Purchase #4 $234.74   7.361%   $252.0192   $252.02   $252.00   $252.00  
  Purchase #5 $102.84   7.405%   $110.4553   $110.46   $110.45   $110.50  
  Purchase #6 $249.72   9.603%   $273.7006   $273.70   $273.70   $273.70  
  Purchase #7 $144.58   4.699%   $151.3738   $151.37   $151.35   $151.40  
  7 purchase totals = $1,302.33       $1,414.2779   $1,414.28   $1,414.20   $1,414.30