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 $189.58   8.291%   $205.2981   $205.30   $205.30   $205.30  
  Purchase #2 $207.81   9.254%   $227.0407   $227.04   $227.05   $227.00  
  Purchase #3 $73.51   9.699%   $80.6397   $80.64   $80.65   $80.60  
  Purchase #4 $41.64   8.868%   $45.3326   $45.33   $45.35   $45.30  
  Purchase #5 $104.97   5.856%   $111.117   $111.12   $111.10   $111.10  
  Purchase #6 $240.34   13.844%   $273.6127   $273.61   $273.60   $273.60  
  Purchase #7 $137.93   8.213%   $149.2582   $149.26   $149.25   $149.30  
  7 purchase totals = $995.78       $1,092.2990   $1,092.30   $1,092.30   $1,092.20