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 $233.69   6.302%   $248.4171   $248.42   $248.40   $248.40  
  Purchase #2 $130.92   9.796%   $143.7449   $143.74   $143.75   $143.70  
  Purchase #3 $160.99   3.212%   $166.161   $166.16   $166.15   $166.20  
  Purchase #4 $66.62   9.237%   $72.7737   $72.77   $72.75   $72.80  
  Purchase #5 $225.42   3.215%   $232.6673   $232.67   $232.65   $232.70  
  Purchase #6 $45.85   12.120%   $51.407   $51.41   $51.40   $51.40  
  Purchase #7 $131.51   10.293%   $145.0463   $145.05   $145.05   $145.00  
  7 purchase totals = $995.00       $1,060.2173   $1,060.22   $1,060.15   $1,060.20