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 $201.83   8.801%   $219.5931   $219.59   $219.60   $219.60  
  Purchase #2 $120.34   11.345%   $133.9926   $133.99   $134.00   $134.00  
  Purchase #3 $36.87   7.394%   $39.5962   $39.60   $39.60   $39.60  
  Purchase #4 $197.64   5.274%   $208.0635   $208.06   $208.05   $208.10  
  Purchase #5 $233.97   7.421%   $251.3329   $251.33   $251.35   $251.30  
  Purchase #6 $81.43   7.257%   $87.3394   $87.34   $87.35   $87.30  
  Purchase #7 $69.97   9.707%   $76.762   $76.76   $76.75   $76.80  
  7 purchase totals = $942.05       $1,016.6797   $1,016.67   $1,016.70   $1,016.70