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 $59.26   8.651%   $64.3866   $64.39   $64.40   $64.40  
  Purchase #2 $103.41   12.156%   $115.9805   $115.98   $116.00   $116.00  
  Purchase #3 $45.97   7.153%   $49.2582   $49.26   $49.25   $49.30  
  Purchase #4 $206.81   10.622%   $228.7774   $228.78   $228.80   $228.80  
  Purchase #5 $187.87   11.260%   $209.0242   $209.02   $209.00   $209.00  
  Purchase #6 $241.72   13.212%   $273.656   $273.66   $273.65   $273.70  
  Purchase #7 $62.44   8.606%   $67.8136   $67.81   $67.80   $67.80  
  7 purchase totals = $907.48       $1,008.8965   $1,008.90   $1,008.90   $1,009.00