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 $204.63   10.591%   $226.3024   $226.30   $226.30   $226.30  
  Purchase #2 $250.83   9.299%   $274.1547   $274.15   $274.15   $274.20  
  Purchase #3 $115.74   8.568%   $125.6566   $125.66   $125.65   $125.70  
  Purchase #4 $35.30   9.111%   $38.5162   $38.52   $38.50   $38.50  
  Purchase #5 $129.44   9.727%   $142.0306   $142.03   $142.05   $142.00  
  Purchase #6 $250.89   13.119%   $283.8043   $283.80   $283.80   $283.80  
  Purchase #7 $181.43   6.640%   $193.477   $193.48   $193.50   $193.50  
  7 purchase totals = $1,168.26       $1,283.9418   $1,283.94   $1,283.95   $1,284.00