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 $71.91   6.194%   $76.3641   $76.36   $76.35   $76.40  
  Purchase #2 $103.82   7.635%   $111.7467   $111.75   $111.75   $111.70  
  Purchase #3 $174.47   3.652%   $180.8416   $180.84   $180.85   $180.80  
  Purchase #4 $131.91   11.595%   $147.205   $147.21   $147.20   $147.20  
  Purchase #5 $200.98   6.639%   $214.3231   $214.32   $214.30   $214.30  
  Purchase #6 $140.81   11.829%   $157.4664   $157.47   $157.45   $157.50  
  Purchase #7 $119.38   8.439%   $129.4545   $129.45   $129.45   $129.50  
  7 purchase totals = $943.28       $1,017.4014   $1,017.40   $1,017.35   $1,017.40