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 $125.64   6.858%   $134.2564   $134.26   $134.25   $134.30  
  Purchase #2 $162.97   8.873%   $177.4303   $177.43   $177.45   $177.40  
  Purchase #3 $241.43   4.484%   $252.2557   $252.26   $252.25   $252.30  
  Purchase #4 $47.82   6.124%   $50.7485   $50.75   $50.75   $50.70  
  Purchase #5 $130.64   8.795%   $142.1298   $142.13   $142.15   $142.10  
  Purchase #6 $129.78   12.237%   $145.6612   $145.66   $145.65   $145.70  
  Purchase #7 $101.42   10.215%   $111.7801   $111.78   $111.80   $111.80  
  7 purchase totals = $939.70       $1,014.2620   $1,014.27   $1,014.30   $1,014.30