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 $119.55   11.822%   $133.6832   $133.68   $133.70   $133.70  
  Purchase #2 $235.94   13.335%   $267.4026   $267.40   $267.40   $267.40  
  Purchase #3 $33.43   3.404%   $34.568   $34.57   $34.55   $34.60  
  Purchase #4 $90.94   6.440%   $96.7965   $96.80   $96.80   $96.80  
  Purchase #5 $227.65   3.443%   $235.488   $235.49   $235.50   $235.50  
  Purchase #6 $116.79   4.677%   $122.2523   $122.25   $122.25   $122.30  
  Purchase #7 $30.66   3.638%   $31.7754   $31.78   $31.80   $31.80  
  7 purchase totals = $854.96       $921.9660   $921.97   $922.00   $922.10