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 $32.68   12.758%   $36.8493   $36.85   $36.85   $36.80  
  Purchase #2 $182.64   9.180%   $199.4064   $199.41   $199.40   $199.40  
  Purchase #3 $62.99   13.359%   $71.4048   $71.40   $71.40   $71.40  
  Purchase #4 $172.74   3.315%   $178.4663   $178.47   $178.45   $178.50  
  Purchase #5 $218.29   12.207%   $244.9367   $244.94   $244.95   $244.90  
  Purchase #6 $60.75   7.865%   $65.528   $65.53   $65.55   $65.50  
  Purchase #7 $208.91   5.811%   $221.0498   $221.05   $221.05   $221.00  
  7 purchase totals = $939.00       $1,017.6413   $1,017.65   $1,017.65   $1,017.50