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 $235.94   10.117%   $259.81   $259.81   $259.80   $259.80  
  Purchase #2 $173.61   11.363%   $193.3373   $193.34   $193.35   $193.30  
  Purchase #3 $62.97   11.213%   $70.0308   $70.03   $70.05   $70.00  
  Purchase #4 $148.49   12.631%   $167.2458   $167.25   $167.25   $167.20  
  Purchase #5 $154.44   4.277%   $161.0454   $161.05   $161.05   $161.00  
  Purchase #6 $146.65   10.141%   $161.5218   $161.52   $161.50   $161.50  
  Purchase #7 $144.83   9.847%   $159.0914   $159.09   $159.10   $159.10  
  7 purchase totals = $1,066.93       $1,172.0825   $1,172.09   $1,172.10   $1,171.90