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 $90.85   4.117%   $94.5903   $94.59   $94.60   $94.60  
  Purchase #2 $230.91   13.641%   $262.4084   $262.41   $262.40   $262.40  
  Purchase #3 $179.47   12.696%   $202.2555   $202.26   $202.25   $202.30  
  Purchase #4 $71.42   12.318%   $80.2175   $80.22   $80.20   $80.20  
  Purchase #5 $49.33   13.339%   $55.9101   $55.91   $55.90   $55.90  
  Purchase #6 $55.33   10.326%   $61.0434   $61.04   $61.05   $61.00  
  Purchase #7 $227.42   11.598%   $253.7962   $253.80   $253.80   $253.80  
  7 purchase totals = $904.73       $1,010.2214   $1,010.23   $1,010.20   $1,010.20