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 $159.44   13.478%   $180.9293   $180.93   $180.95   $180.90  
  Purchase #2 $108.34   12.224%   $121.5835   $121.58   $121.60   $121.60  
  Purchase #3 $148.89   12.871%   $168.0536   $168.05   $168.05   $168.10  
  Purchase #4 $126.80   12.731%   $142.9429   $142.94   $142.95   $142.90  
  Purchase #5 $47.87   5.194%   $50.3564   $50.36   $50.35   $50.40  
  Purchase #6 $56.48   9.768%   $61.997   $62.00   $62.00   $62.00  
  Purchase #7 $142.85   11.842%   $159.7663   $159.77   $159.75   $159.80  
  7 purchase totals = $790.67       $885.6290   $885.63   $885.65   $885.70