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 $200.59   3.361%   $207.3318   $207.33   $207.35   $207.30  
  Purchase #2 $52.90   7.292%   $56.7575   $56.76   $56.75   $56.80  
  Purchase #3 $151.68   7.850%   $163.5869   $163.59   $163.60   $163.60  
  Purchase #4 $182.26   3.345%   $188.3566   $188.36   $188.35   $188.40  
  Purchase #5 $149.99   8.226%   $162.3282   $162.33   $162.35   $162.30  
  Purchase #6 $242.99   12.293%   $272.8608   $272.86   $272.85   $272.90  
  Purchase #7 $89.50   11.870%   $100.1237   $100.12   $100.10   $100.10  
  7 purchase totals = $1,069.91       $1,151.3455   $1,151.35   $1,151.35   $1,151.40