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 $40.55   8.839%   $44.1342   $44.13   $44.15   $44.10  
  Purchase #2 $16.78   4.301%   $17.5017   $17.50   $17.50   $17.50  
  Purchase #3 $45.88   4.797%   $48.0809   $48.08   $48.10   $48.10  
  Purchase #4 $186.77   7.646%   $201.0504   $201.05   $201.05   $201.10  
  Purchase #5 $57.93   8.401%   $62.7967   $62.80   $62.80   $62.80  
  Purchase #6 $46.51   10.590%   $51.4354   $51.44   $51.45   $51.40  
  Purchase #7 $121.92   7.472%   $131.0299   $131.03   $131.05   $131.00  
  7 purchase totals = $516.34       $556.0292   $556.03   $556.10   $556.00