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 $223.80   9.564%   $245.2042   $245.20   $245.20   $245.20  
  Purchase #2 $162.66   4.715%   $170.3294   $170.33   $170.35   $170.30  
  Purchase #3 $35.86   6.780%   $38.2913   $38.29   $38.30   $38.30  
  Purchase #4 $64.71   10.626%   $71.5861   $71.59   $71.60   $71.60  
  Purchase #5 $50.68   6.547%   $53.998   $54.00   $54.00   $54.00  
  Purchase #6 $26.43   10.840%   $29.295   $29.30   $29.30   $29.30  
  Purchase #7 $39.98   11.251%   $44.4781   $44.48   $44.50   $44.50  
  7 purchase totals = $604.12       $653.1821   $653.19   $653.25   $653.20