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 $192.45   8.724%   $209.2393   $209.24   $209.25   $209.20  
  Purchase #2 $119.78   12.717%   $135.0124   $135.01   $135.00   $135.00  
  Purchase #3 $183.55   11.605%   $204.851   $204.85   $204.85   $204.90  
  Purchase #4 $114.30   7.511%   $122.8851   $122.89   $122.90   $122.90  
  Purchase #5 $64.65   10.167%   $71.223   $71.22   $71.20   $71.20  
  Purchase #6 $147.28   5.246%   $155.0063   $155.01   $155.00   $155.00  
  Purchase #7 $118.93   7.770%   $128.1709   $128.17   $128.15   $128.20  
  7 purchase totals = $940.94       $1,026.3880   $1,026.39   $1,026.35   $1,026.40