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 $227.25   11.739%   $253.9269   $253.93   $253.95   $253.90  
  Purchase #2 $10.75   7.173%   $11.5211   $11.52   $11.50   $11.50  
  Purchase #3 $79.47   3.269%   $82.0679   $82.07   $82.05   $82.10  
  Purchase #4 $165.98   12.170%   $186.1798   $186.18   $186.20   $186.20  
  Purchase #5 $154.32   4.823%   $161.7629   $161.76   $161.75   $161.80  
  Purchase #6 $56.50   7.835%   $60.9268   $60.93   $60.95   $60.90  
  Purchase #7 $32.86   8.532%   $35.6636   $35.66   $35.65   $35.70  
  7 purchase totals = $727.13       $792.0490   $792.05   $792.05   $792.10