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 $203.36   12.379%   $228.5339   $228.53   $228.55   $228.50  
  Purchase #2 $149.55   11.467%   $166.6989   $166.70   $166.70   $166.70  
  Purchase #3 $194.34   11.791%   $217.2546   $217.25   $217.25   $217.30  
  Purchase #4 $92.58   9.829%   $101.6797   $101.68   $101.70   $101.70  
  Purchase #5 $71.56   3.493%   $74.0596   $74.06   $74.05   $74.10  
  Purchase #6 $166.87   7.273%   $179.0065   $179.01   $179.00   $179.00  
  Purchase #7 $47.67   5.267%   $50.1808   $50.18   $50.20   $50.20  
  7 purchase totals = $925.93       $1,017.4140   $1,017.41   $1,017.45   $1,017.50