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 $163.59   10.652%   $181.0156   $181.02   $181.00   $181.00  
  Purchase #2 $226.85   3.693%   $235.2276   $235.23   $235.25   $235.20  
  Purchase #3 $55.78   5.447%   $58.8183   $58.82   $58.80   $58.80  
  Purchase #4 $202.45   7.829%   $218.2998   $218.30   $218.30   $218.30  
  Purchase #5 $24.49   13.477%   $27.7905   $27.79   $27.80   $27.80  
  Purchase #6 $239.68   12.854%   $270.4885   $270.49   $270.50   $270.50  
  Purchase #7 $32.82   5.850%   $34.74   $34.74   $34.75   $34.70  
  7 purchase totals = $945.66       $1,026.3803   $1,026.39   $1,026.40   $1,026.30