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 $69.87   10.523%   $77.2224   $77.22   $77.20   $77.20  
  Purchase #2 $109.99   11.132%   $122.2341   $122.23   $122.25   $122.20  
  Purchase #3 $175.41   4.293%   $182.9404   $182.94   $182.95   $182.90  
  Purchase #4 $65.30   13.694%   $74.2422   $74.24   $74.25   $74.20  
  Purchase #5 $202.62   8.373%   $219.5854   $219.59   $219.60   $219.60  
  Purchase #6 $233.66   4.618%   $244.4504   $244.45   $244.45   $244.50  
  Purchase #7 $109.66   9.292%   $119.8496   $119.85   $119.85   $119.80  
  7 purchase totals = $966.51       $1,040.5245   $1,040.52   $1,040.55   $1,040.40