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 $107.58   10.868%   $119.2718   $119.27   $119.25   $119.30  
  Purchase #2 $144.48   3.310%   $149.2623   $149.26   $149.25   $149.30  
  Purchase #3 $176.91   3.815%   $183.6591   $183.66   $183.65   $183.70  
  Purchase #4 $246.29   11.214%   $273.909   $273.91   $273.90   $273.90  
  Purchase #5 $37.49   11.475%   $41.792   $41.79   $41.80   $41.80  
  Purchase #6 $232.58   7.641%   $250.3514   $250.35   $250.35   $250.40  
  Purchase #7 $147.47   10.139%   $162.422   $162.42   $162.40   $162.40  
  7 purchase totals = $1,092.80       $1,180.6676   $1,180.66   $1,180.60   $1,180.80