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 $150.42   11.555%   $167.801   $167.80   $167.80   $167.80  
  Purchase #2 $80.25   12.398%   $90.1994   $90.20   $90.20   $90.20  
  Purchase #3 $190.93   5.610%   $201.6412   $201.64   $201.65   $201.60  
  Purchase #4 $72.26   4.280%   $75.3527   $75.35   $75.35   $75.40  
  Purchase #5 $215.87   5.322%   $227.3586   $227.36   $227.35   $227.40  
  Purchase #6 $208.60   4.188%   $217.3362   $217.34   $217.35   $217.30  
  Purchase #7 $143.37   7.784%   $154.5299   $154.53   $154.55   $154.50  
  7 purchase totals = $1,061.70       $1,134.2190   $1,134.22   $1,134.25   $1,134.20