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 $56.60   11.623%   $63.1786   $63.18   $63.20   $63.20  
  Purchase #2 $222.75   4.458%   $232.6802   $232.68   $232.70   $232.70  
  Purchase #3 $156.94   3.688%   $162.7279   $162.73   $162.75   $162.70  
  Purchase #4 $21.66   9.166%   $23.6454   $23.65   $23.65   $23.60  
  Purchase #5 $211.25   6.190%   $224.3264   $224.33   $224.35   $224.30  
  Purchase #6 $83.98   8.517%   $91.1326   $91.13   $91.15   $91.10  
  Purchase #7 $46.85   9.482%   $51.2923   $51.29   $51.30   $51.30  
  7 purchase totals = $800.03       $848.9834   $848.99   $849.10   $848.90