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 $61.39   5.774%   $64.9347   $64.93   $64.95   $64.90  
  Purchase #2 $189.84   13.229%   $214.9539   $214.95   $214.95   $215.00  
  Purchase #3 $50.33   4.833%   $52.7624   $52.76   $52.75   $52.80  
  Purchase #4 $225.55   12.769%   $254.3505   $254.35   $254.35   $254.40  
  Purchase #5 $142.73   6.750%   $152.3643   $152.36   $152.35   $152.40  
  Purchase #6 $21.90   9.710%   $24.0265   $24.03   $24.05   $24.00  
  Purchase #7 $65.61   11.153%   $72.9275   $72.93   $72.95   $72.90  
  7 purchase totals = $757.35       $836.3198   $836.31   $836.35   $836.40